Centritugal Force MESSRS. EDITORS :—Some of your correspondents having recently suggested centrifugal force as one of the causes of the open Polar Sea, and of tlie varying hight of the tides in different places, might not a brief examination of the nature of this force, and some of its effects as induced by the rotation of the earth bo of interest to your readers ? The tendency of any particle of matter once set in motion, is to continue to move forward in a straight line, but if an external force is brought to bear in such manner as to constrain it to move in a curved line it will meet with a certain resistance, which is denominated centrifugal force. The amount of this force, as compared with that of gravitation at the earth's surface, can be found by squaring the distance in feet, moved by the body in one second, dividing by the radius of the curve described, and by 3219 feet, the velocity which a falling body acquires in one second. Therefore, centrifugal force is in the direct ratio of the square of the velocity, and the inverse ratio of the radius. If we apply the foregoing rule to the earth, we shall find that, at the equator, any object is drawn upward by this force, with a power equal to -\g of that of gravitation. In other words, the weight of all matter at the equator would be about that amount more, were it not for the rotation of the earth on its axis. As there can be no centrifugal force at the poles, gravitation has there its full effect. It will be seen that this difference in the central forces of the earth would induce it to assume the form of a spheroid with its polar radius -jl-g-less than its equatorial. Actual geodetic measurements, however, make it 1/300 less, showing that this effect is in part counteracted by other causes. Let us now glance at the effect of centrifugal force at the 45th parallel of north latitude. Here we find that the radius of rotation has decreased (being expressed by the cosine of the latitude), and that the direction of the force is not in a plane perpendicular to the earth's surface, but is inclined toward the south at an angle equal to the latitude. If at this point a plumb line be suspended 100 feet in length, and acted upon by gravitation alone, it would come to rest in a direction pointing to the earth's center; but by calculation, we find that the earth's rotation will exert a force on the body thus sus-pende, equal to 1-410 of its weight, tending to lift it and carry it southwardly at an angle of 45 . By resolving this force, we find it equal to 1/580 acting in a horizontal direction, which in a plumb line 100 feet long, is sufficient to produce a deflection of 4.14 inches, or twelve minutes of a degree. This deflection of the plumb line is greatest at latitude 45 , and grows less as we proceed toward the equator or the poles. But does it follow from this that all our high buildings— whose walls are coincident with the plumb line—are not perpendicular to the water level ? By no means. For if we calculate the influence which, centrifugal force exerts upon water, we shall find that it is in equilibrium only when its surface forms a right angle with the direction of the plumb line, and coincides with th"e spheroid form of the earth. Whoever gives this subject a close examination, will perceive that, so long as the velocity of the earth in its diurnal revolutions, remains constant, no effect will be produced on the currents of the ocean or on the tides. Boston, Mass. JOHN M. AENOLD. Shot-Gun Barrels MESSES. EDITOES :—In your issue of January 28d, page 55, " K. P. S," of Ohio, asks, " What is the best length for shotgun barrels ?" I have had considerable experience in such matters, and perhaps might give him a hint. For rabbits or partridges, a double-barreled gun need not be more than 24-in. barrels and 14 gage. For ducking on the Chesapeake, where they shoot from stands, the best is a 4-foot barrel (single), and of 5 gage. For ducking on the eastern bays, the best is a double gun, with 32-in. or 34-in. barrels and 9 gage. The best for all kinds of shooting is a 14 gage, 30-in. barrels of from 10 to 14 lbs. weight. I do not agree with you that 16 or 18 inches will produce as good an effect as the longer ones. First, there is more recoil. Second, the muzzle will throw up at the discharge, spoiling the shot Third, the charge gets out of the barrel too quick, or, in other words, before the powder is all ignited. Take two guns equal other-! wise, one 16-in. and one 30-in. The 16-in. will throw out part of the powder unconsumed (which may be seen if fired across snow); the other one will not. If the gun tapers from muzzle to "breech, it will scatter, or if vice versa, it will give and cut the shot, and will, in course of time, spring the barrels. I have had a good deal of experience as a gunsmith, and being my-soif a gunner, I have tried almost all kinds of guns, and the statements I have given you I have always found to be correct. Plymouth, Mass. THOS. MARTEST. Liquid Fuel and American Inventions In France MESSES. EDITOES :—As notice of the more valuable discoveries in the field of science commonly appears first in the columns of your journal, I desire to lay before its readers a few facts coming within my own observation on the above subject. Through the kindness of the proprietors of an immensely large boiler and machine establishment in Paris, I was enabled to witness recently the practical working of liquid fuel, in a boiler running an engine of- 15-horse power. There were also present scientific engineers from the United States, Great Britain, Russia, and France, as well as dignitaries of the Empire, and numerous other gentlemen. The oil, or the refuse of oil, was of an inferior kind, and every other circumstance was purposely so arranged as to make the exhibition a test under extraordinary difficulties. After lighting, steam was quickly obtained and run up to the extreme limits and there held throughout ,"the engine working its full capacity on less than 2 gallons of oil per hour, evaporating 18 to the pound of fuel. After getting well under way the fire was safely left by the hour to-regulate and fire itself while the fireman quietly smoked"" his pipe at a distance ; this showing that one man could easily attend five or six liquid fuel fires, whereas if fired with coal, would require ten or a' dozen men. A singular phenomenon was observed during the latter part of the day. After several hours running and everything well heated,,it was found that the ratio of oil consumed to the evaporation obtained gradually diminished, until at the close of the day it required hardly 50 per cent of the amount used at first, to produce equal results, apparently with all the other conditions unchanged. I am told that this is a fixed feature of this invention. I leave it to some of your curious readers to explain. Now let us exhibit facts, leave others to draw conclusions. This liquid fuel costs here but 3 cents per gallon and it is officially demonstrated that the article in different grades can be had and even produced almost anywhere at a price tun for tun at a lower average cost than coal. A tun of coal will occupy 44 cubic feet of a ships bunkers, Liquid fuel only 33. One pound of oil by this invention will evaporate nearly thrice, say twice as much water as a pound of coal; the former requiring in using but a"bout one-tenth part the labor of coal, the element perfectly controllable, the apparatus simple, the supply inexhaustible. Why then is not the much] invited question of liquid hydrocarbon as a fuel a perfect success ? This was indeed the unanimous verdict of all tlie practical and scientific gentlemen present 'there. Indeed an elaborate report fully indorsing the above, has been made to the Emperur by a high official well known in the States. As an American I am happy to say the inventor of this system is also an American, invited here to test it; having dons 50 satisfactorily, capitalists have bought the patent for several European countries, at a high figure. The value of this improvement as a steam generator having been definitely settled, the plans are now being made up for applying liquid fuel to making iron, steel, smelting over, working in metallurgy generally, for which the inventor claims it is even more valuable. It has been already demonstrated that all metals can he- brought to the required heat by this system in less than half the time than by any other means. All inflax of cold air through opening doors upon the molten metal is then avoided, but above, all, the effect of the sulphur, phosphorus, etc., found in all coal, and so deleterious to the texture of the metals, will be entirely obviated by the use of this new fuel, -while the most intense heat will be obtained beside securing important chemical results. And here I should remark that the inventor has designed and patented a series of furnaces and metal baths specially calculated for this fuel, and. which are pronounced much superior to all others. French iron and steel manufacturers, give the whole system their hearty approval, and as above seen are adopting it. You may have noticed in the London Times, lately, several articles on this subject. In conclusion, should I not return to the States too soon, I shall take occasion to give yo'u hereafter a further account of the practical working of liquid fuel, its new field of usefulness. Its entire success however, seems to have been already established. I should have been pleased to refer to names and particulars in this connection ; but,knowing that your reading columns are closed to everything that savors of puffing, I have here confined myself to a plain statement of facts as they are, or may be seen by all. H. H. H., of Brooklyn, N\ T. Paris, France., Jan. 5, 1869. A Reason for Protection MESSES. EDITOES :—In the last number of the SCIENTIFIC AMEEICAN, I notice the question " Does American Industry Need Protection." I wish to suggest a reason for protection which I have never seen connected with the subject—one which appears to me conclusive. It has been estimated that the steam power and machinery of England is equivalent to 600,000,000 of laborers, while the United States has but 300,-000,000. Without protection, England is likely to maintain her great superiority in this respect for a long time. If her steam power could and would consume our agricultural products, there would be some excuse for free trade. We have not onjy her overwhelming number of laborers to compete with, but the overwhelming wealth they have accumulated. The cheap human labor, which has always entered into political economy, is of small account in comparison with the unconsuming slaves of England. It is this superiority which makes protection useless and inoperative there—it is abundant protection in itself. E. M. CHAFFEE. Bridgeport, Conn. Explosion of a Locomotive Boiler-—Was it Steam or Gas ? MESSES. EDITOES :—I have never seen in your columns a report from any one on a boiler explosion. A locomotive which exploded, Dec. 26th, attracted my attention, and as no theory of low water or formation of gas is admissible in this case, the cause of it is I think as I shall state. It was of the usual locomotive type, raised wagon top, and two"19-inch domes. The engine stalled with a pressure of 100 lbs., the blower was used until 130 lbs. was reached, the usual " off brakes " was blown, and the engineer .told a brakeman, who was on the engine, to close the blower, and was in the act of pulling the throttle when she exploded, the brakeman said, " it was like pulling a trigger" " The boiler gave way in the gusset or throat sheet, about 10 or 12 inches below center of boiler. There was an internal defect in. the sheet at that place; it was not welded but laid in separate layers each probably not over 1-16 thick. The force of the explosion was upward and to the right; as the defective place was immediately opposite a driving wheel, it forced it from axle in fragments, cutting the tire like lead. All the cylinder part of boiler was torn to pieces, and the wagon top to dome joint. The iron is torn in every direction, but there is not a place where the riveting has given way and where the sheets are torn, the fracture ceases when it comes to a line of riveting. The iron is not over J thick, and is of good quality, with the exception of two or kthree defective places that are internal defects that the most careful examination could not have detected. The cause of the explosion was weakness of the boiler, which is probably the cause of all the explosions. Water at a temperature of 212 makes 1700 times its volume of steam, which at a pressure of 100 lbs. is only 395, and at 130 lbs. but 233. The blower was -J inch diameter, and steam issued from it at the rate of 1000 feet per second. In shutting off blower, this current of steam was checked; while a gush of of flame filled the firebox and flues, by being checked by the closing of the blast. As the weakest point always yields first, and the steam and water thus liberated expanded, as is shown above, and the flow took place towards the vent, the momentum of the water with its pressure tore everything in its way until its force was spent. This is apparent from the flues, which are spread out and scattered as if to give room for the water to escape, and the outside flues are flattened as if they had been forced against the boiler before it gave way. The force exerted is something wonderful, when we take into account that the wheel had been put on with a pressure of 60,000 lbs., and a well fitted key driven in afterwards and then the tire shrunk on. The frame, of 4-inch square iron, was broken short off, and the reverse arm weighing probably 100 lbs. was thrown about 500 yards. It may be said that the water or steam is not capable of acting thus, but is not this the same principle as the injector, as well as of the steam pump, where the steam acts directly against the water and forces it in the boiler against the same pressure as started it S Huntsville, Ala [Ojir correspondent is in error as regarding the relative temperature and pressure of steam. According to Regnault the temperature of steam at 100 lbs. pressure is 386 , and at 130 lbs. 355 .—EDS. Discharge of Water -Under Different Heads MESSES. EDITOES :—In a recent issue of the SCIENTIFIC AMEEICAN, in the " Answers to Correspondents," 1 notice you say that " 200 square inches of water under 4-feet head is not equal in quantity or power to 100 square inches under 16-foet head." I have always understood it would not be equal in power, but have always understood that the discharge of water from the same sized opening, in the same time, would vary as the square root of the heads of water under which such opening was placed : that is, the square root of 4-feet head being 2, and the square root of 16-feet head being 4, there would be twice as much water vented under the 16-feet head in the same time from the same opening that there would be under 4-feet head. You would confer a personal favor on me and probably upon many others, by replying to this. The ratk. of contraction may vary a little in your described circumstances, but as there was no mention made of it, I suppose that it did not enter into your calculations, as it does not in mine. T. H. RlSBON, Mount Holly, N. J. [Our correspondent is right in his opinion that the amount of discharge which will take place from equal and geometrically similar apertures, is theoretically proportional to the squares of their respective distances below the surface. The reply to which he refers had no reference to the flow of water under a constant head, hut simply to the statical effect and weight of two columns having specified areas of base and given hights. Eccentric and Crank Combined MESSES. EDITOES:—I noticed in the SCIENTIFIC AMERICAN, page 21, current volume, a week or two ago, under the above heading, a communication from D. H. McCormick in relation to the valve moving apparatiis of the Keewenaw, and in which he has overlooked a very important point, as I think. Two years ago last summer, I was on board the Keewenaw and became very much interested in the valve gear, so much so that I examined it very attentively. Mr. McCormick has correctly described it with the exception that he makes a joint .in the eccentric rod at the point of contact with the fulcrum, which does not exist, or did not when I saw it. I did not discover any slot in the crank, but accounted for the unequal length at different points, by the long connectioa and its elasticity 119 There might have been a slot for the crank pin but I am sure there was no joint in the connection. N. East Saginaw, Mich. Sal Soda and Soda Crystals MESSES. EDITOBS :—From a partial copy of House Reports, 1,349, sent to me some time ago, I noticed the proposal to advance duty on sal soda and soda crystals to one cent per pound, or one-half cent more than actual duty; also to advance duty on caustic soda two cents per pound, or one-half cent more than actual duty ; bleaching powders, now subject to a duty of thirty cents per 100 pounds, to be put on the free list. If it is really the intention of Congress to protect the manufacture of soda salts, duties should be so arranged as to promote competition between the manufacturers of these salts from chloride of sodium and those handling the kryolite monopoly. With the present high price of common salt (chloride of sodium), and the proposed abolition of .duty on bleaching powders, that competition will be rendered impossible ; for, by using chloride of sodium, an immense quantity of muriatic acid (hydrochloric acid) is obtained, which is of little or no value to the manufacturer if he cannot use it in the manufacture of bleaching powders. If, therefore, the duty on soda salts is increased, the duty on bleaching powders should also be proportionately advanced, and in no event should they be put on the free list. There is an able paper, from Dr. Squibb, in reference to soda salts, published in the Pharmaceutical Association Reports for 1867, but the doctor is evidently mistaken in speaking of a California mine of profits to the manufacturers of soda salts from chloride of sodium. At present there is scarcely a margin of profits left to them. It is different, however, with the kryolite monopoly. AN OLD SODA-ASH MANUFACTUBEB. ., Cleveland, Ohio. [Our correspondent's point seems to us well taken.—EDS Four Pounds of Butter from a Gallon of Milk MESSES. BBITOBS : —In a recent issue of your journal allu-sion was made to a newly-discovered butter process, whereby one pound of butter and one gallon of milk was said to produce four pounds of good butter. Your remarks thereon were to the effect that if four pounds of butter were produced, over three pounds must have been put into the vessel from which it was taken. Examination of butter produced by the same process in this city seems to confirm your assertion—the product is not butter, but appeal's to be produced on the same principle as a soap-maker produces soap; in one case one pound of butter and one gallon of milk put into the apparatus, and a powder added, presently out comes the butter. In the other case, the soap-maker puts a certain quantity of fatty matter, and a correct proportion of water; the addition of an alkali produces a union of the opposite substances, and. soap is the result; the action seems to be analogous in each case. Potash produces soft soap, from its strong affinity for moisture ; soda produces hard soap ; it seems probable, therefore, that the powder is a refined preparation of caustic soda. ENTERPRISE Cincinnati, Ohio [Our correspondent is right in his views. The use of alkaline carbonates to make water combine with, and increase the weight of lard is an old trick, and it has now been extended to butter. We understand some of these importers use alum also. It is a striking illustration of the ease with which public imposition can be practiced that such a bare-faced swindle as this can prove successful.—EDS. Efficient Tank, Condenser, and Water Heater MESSES. EDITOEB :—I have written an article embodying a plan of arrangement which I adopted some years ago, and the ideas of which I got from careful readings of the SCIENTIFIC AMEBICAN, and would like to help others to a cheap way of overcoming some difficulties which we meet in the West in driving steam engines. Reading the article on page 60, present volume, by F. W. Bacon, I have been'induced to describe an arrangement I made in 1859 on placing a new boiler in position. Had the flues removed from the old one (18 feet by 40 inches), and the boiler heads fastened up tight; hung this boiler over the new one for a water tank, at a sufficient high* to allow of the boiler being filled from it through the safety valve ; introduced the exhaust pipe from the engine into this tank on the upper side at one end, carried another exhaust pipe from the other end through the side of the engine house into the atmosphere. The force pump was bolted directly to the stand-pipe, the feed water taken from a point about six inches above the bottom of the tank, allowing space for the deposits of sediment. The exhaust steam passing over the surface of the water in the tank kept it at 212 , and owing to short connections between force pump and boiler, reached the latter without any sensible diminution of heat. Some of the advantages of this plan are as follows: The feed water deposited nearly or quite all of its sediment, also a large proportion of the carbonate of lime contained in it; had always a large body of hot water on hand for purposes aside from boiler supply; and its value as a condenser was one of its chief merits. While the supply pump was running, all the exhaust steam was condensed, or a large proportion of it, until the water reached its maximum heat, and after that condensation still went on slowly. The tank could be filled to the level of the second exhaust, and if the pump was not stopped, the surplus water ran out of the pipe ; the force pump being so closely connected to the boiler, friction was prevented, which always attends-feed pipes between the force pump and boiler, and power served thereby. I found it necessary to clean the tank twice a year, and the amount of sediment removed, which, with the ordinary arrangement, would have passed into the boiler, was enormous. This is still in use, and giving perfect satisfaction ; and during the nine years that I used it, I did not spend a dime in repairs. Though I suppose this plan has been used by others, still I never saw it, and recommend it to those who cannot afford elaborate apparatus, as a cheap and effective method of combining tank, condenser, and feed-water heater, and also as a receptacle for the deposit of impurities that would otherwise pass into the boiler. Another advantage I have not mentioned is this: On extremely cold nights and during the cessation of work on the Sabbath, the large body of water in the tank will remain warm, thus keeping up the temperature in the engine house and preventing the freezing of pumps, pipes, etc. T. L. Central College, Franklin Co., Ohio. . Testing Steam Engines MESSES. EDITOBS :—I have been too much occupied to notice sooner Mr. F. W. Bacon's criticism on my articles on the above subject I am sorry that Mr. B. considered it necessary to the successful presentation of his views to recall some visit to a repair shop, and suggest or imply some connection between what he saw there, and other matters which could not possibly have occurred there. The gentleman, for want of better argument, has fallen into a very common mistake which would have been far more clearly expressed had he said " I don't believe the statements, therefore they are not true." Lilfe him, I once did not believe that the inaccuracies spoken of on page'308 of your last volume were of any practical value. I waited, however, till I experimented before expressing my opinion in print. The fact that I used an English instrument in those particular experiments showed no want of confidence in American instruments. I have used all kinds and it is unnecessary to say that the Yankees can do as good work as any foreigner. The derangement mentioned, namely, that the pencil does not move in an exact line with the axis of the paper drum, is a common one to all indicators wherever manufaclured. It is of less consequence than one would at first suppose, so long as the pencil gets a good bearing on the drum, for it in no way affects the accuracy of the diagrams when the measurements are made in lines parallel to the movement of the pencil. The defect is easily remedied by springing the bracket which carries the drum. The remarks of Mr. B. about friction are in the main correct. Nothing is learned by criticising mere forms of expression. He acknowledges that the indicator does not show separately the friction of the engine and of the load. This is the main fact I wished to bring out, so it is equally correct to say that the indicator does not show the useful work an engine is capable of performing. CHAS. E. EMERY. New York City. Is Resistance to Speed of Steamers as the Square or Cube of the Velocity? MESSES. EDITOBS :—A correspondent of the SCIENTIFIC AMEBICAN", of 24th January, page 70, finds the above a " vexed question." To the present writer it is plain. The power is the steam used in a given lime and .is as the cube of the velocity ; but for a given distance as the square, the time of using the steam being shortened as the difference between the square and the cube. To double the speed, four times the force on tlie piston, and quantity of steam are required, when the doubled velocity of piston and wheel demands also a double supply of the four-times force, making a consumption of eight times, or as the cube. If tho ordinary time of a steamer were ten days from New York to Liverpool, to perform the trip in five days would require a supply of four times the coal and steam over the ten day's supply, or as the square, but the consumption of steam during five days, would be at the rate of eight times, or as the cube of velocity. T. W. BAKEWELL. Pittsburgh, Pa, Eccentric with Crank Combined MESSES. EDITOBS:—On page 69, Vol. XX., Mr. Palmer wants me to explain my diagram, which he says won't work unless there is something on the shaft not shown on the engraving to throw it over the center. There is something on the shafts to comply with this requirement in the shape of a crank on either end of the small shaft, X, with two double rods, and an eccentric on either side of the main crank. But they are set at right angles to each other, so that when one crank is on the center the other is at a point furthest from it, thus producing a steady movement and in some manner governing the engine. D. A. MCCOEMICK. Safety In the Use of Kerosene Lamps MESSES. EDITOES :—In the days of camphene there used to be a safety arrangement of wire gauze containing the wick, and attached to the inside of the lamp. Why is it that our kerosene lamp makers do not now use this simple safety contrivance ? The feeling of security would be cheaply bought at the trifle additional expense. The gauze was also used on the nozzle and mouth of the can for filling, and also covered the receptacle and cock in the store. Many lives, much suffering, and many dollars might ere this have been saved, if our people had the sense to demand it. T. C. Boston, Mass. An Appreciative Client MESSES. MUNN & Co., SIHS:—Having received the Letters Patent from Washington, dated January 26th, 1869,1 now take great pleasure in returning my sincere thanks to you forattending to the claim which I entrusted to your care; and should I ever want other patents, never would I look fora more reliable, careful, or experienced counsel than you. In the future I shall recommend all that are in want of such aid to you. F. SIDNEY TOWNSEND. South Seaville, N. Y. Why Don&t Boys Learn Trades ? The Philadelphia Ledger justly remarks that the present generation of young men seems to have a strong aversion to every kind of trade, business, calling, or occupation that requires manual labor, and an equal strong tendency toward some so-called "genteel" employment or profession. The result is seen in a superabundance of elegant penmen, bookkeepers, and clerks of every kind who can get no employment, and are wasting their lives in the vain pursuit of what is not to be had ; and a terrible overstock of lawyers without practice and doctors without patients. The passion on the part of the boys and young men to be clerks, office attendants, messengers, anything, so that it is not work of the kind that will make them mechanics or tradesmen, is a deplorable sight to those who have full opportunities to see the distressing effects of it in the struggle for such employments "by those unfortunates who have put it out of their power to do anything else by neglecting to learn some permanent trade or business in which trained skill can always be turned to account. The applications for clerkships and similar positions in large establishments are numerous beyond anything that would be thought of by those who have no chance to witness it. Parents and relatives, as well as the boys and young men themselves, seem to be afflicted with the same infatuation. To all such we say, that the most unwise advice you can give to your boy is to encourage him to be a clerk cr a bookkeeper. At the beet, it is not a well-paid occupation. Very frequently it is among the very poorest. This is the case when the clerk is fortunate enough to be employed ; but if he should happen to be cut of place, then comes the weary search, the fearful struggle with the thousands of others looking for places, the -never-ending disappointments, tho hope deferred that makes the heart sick, the strife with poverty, the humiliations that take all the manhood out of the poor souls, the privations and sufferings of those who depend upon his earnings, and who have no resource when he is earning nothing. No farther, no mother, no relative should wish to see their boys or kindred wasting their young lives in striving after the genteel positions that bring such trials and privations upon them in after life. How do these deplorably false notions as to choice of occupation get into the heads of boys ? Why do they or their parents consider it more " genteel " or desirable to run errands, sweep out offices, make fires, copy letters, etc., than to make hats or shoes, or lay bricks, or wield the saw or jackplane, or handle the machinist's file, or the blacksmith's hammer ? We have heard that some of them get these notions at school. If this be true, it is a sad perversion of the means of. education provided for our youth, which are intended to make them useful, as well as intelligent members of society, and not useless drags and drones. Should it be so, that the present generation of boys get it into their heads that, because they have more school learning and book accomplishment than their fathers had, they must therefore look down upon the trades that require skill and handicraft, and whose productions make up the vast mass of the wealth of .every country, then it is time for the controllers and the directors to have the interior walls of our school heuses covered with maxims and mottoes warning them against the fatal error. Coral Reefs Prof. Ebell, of New Haven, recently delivered a lecture at the Cooper Institute upon corals, mollusks, snails, and cuttlefish. These animals, it was said, belong to the class of radi-ata. The reason for thus designating them was given, and illustrated with diagrams. The coral was described as belonging to this class-of radiata. There were three conditions mentioned as necessary to the growth of these animals and the productions of coral islands. First, a temperature of the water at or above sixty degrees. They will not live where the water is below that. They are found distributed in the ocean, not according to the lines of latitude, but according as the temperature is modified by ocean currents. Second, a depth of water not less than thirty feet, and not over one hundred is required. The structure of the animal is such that it cannot live at a greater or less depth, or at all events have a vigorous growth. A few are found at a less depth, but of so frail a development as to be broken off by the motion of the sea. The last essential is that the water be pure. Coral islands are formed around the base of a mountain wholly or in part submerged. The form of the growth of these island's is perpendicular toward the water, and shelving toward the land. These islands never rise nearer to the surface than thirty feet by the action of the coral animals themselves. Any nearer approach to the surface, or projection above it is attributable to the deposit, by the waves, of the frailer kind of coral found, at a less depth than thirty ieet, and broken off from the rocks by the action of the water. Sometimes the mountain sinks below the water, and then the coral deposits are seen in the form of a circle, with a lake or lagoon in the center. These lagoons are sometimes taken advantage of in the production of salt, water being.1 et in and retained until it has evaporated and left a residuum of salt. Turk's Island salt, so familiar to. commerce, is obtained in this way. From the consideration of corals the lecturer proceeded to the consideration of jelly fish, and thence to mollusks, and last of all, the cephalapods, to which class the cuttlefish belongs, was considered. The lecture was illustrated throughout with extemporized drawings on the blackboard, and afterward by more elaborate rep... resentations by means of the magic lantern. 120 Improvement in Devices for Guiding and Trueing Circular Saws Large circular saws, when running swiftly, are liable to oscillate or spring1 at the' periphery, or to describe a wavy or curved vertical line rather than a right vertical line. " The cause is yet in doubt, but whether owing to unevenness in the texture of the plate, difference in its temperature by difference of speed between the periphery and center, or the effect of occasional and accidental obstructions, the fact remains, and a necessity exists for some device to steady the saw in working. This object is sought to be attained by the device shown in the accompanying illustration, marked Fig. 1. The guide is of iron, and is secured to the saw frame by the adjustable standard, A, on which the supporting arm, B,is bolted at the point shown in the engraving, or at A, as best adapted to the build of the saw frame. This arm sustains the guide proper, C, having two pivoted arms, D, which swing on the bolts, E, as pivots, and carry, each, a steady pin or roller, F, of wood, seen in the engraving impinging against the surface of a saw, a segment of which, with Emerson's inserted teeth; is represented. The pivoted arms, , D, extend back under the cap, ' C, to the rear and receive between them a U-shaped spring by which the jaws or ends carrying the pins, F, are forced together. They are brought apart or adjusted by set ssrews, G, one on either side, and vibration of the jaws to correspond with that of the saw, is secured by the screws and check nuts, H. It will be seen that the vibration given to the pins, F, will allow the saw to retain its course, while cutting, when the carriage runs out of line, thus saving a great amount of power. The device will also prevent a saw that is sprung from'wavering or rattling. The pins or bearers, F, may be adjusted while the saw is running without endangering the hands. Every provision is made for varying the stand or guide in higrht or horizontal position. Fig. 2 represents the jointer, shown in Fig. 1 attached to the under side of the guide by the bolt I, Fig. 1, and A, Fig. 2. A piece of mill file, B, is clamped on a slide that may be moved forward and backward by a screw, C, turned by the knob or hand wheel, D. This is permanently attached to the guide ready for instant use when jointing is required, and out of the way when the saw is in use. It may also be made to be used independent of the guide if required. Fig. 8, is a gage and square for setting and filing saw teeth, or rather for determining the set or swage of the teeth. The points, A and B, rest against the side of the saw and the teeth points revolve between the set screws, C. D is a wrench for setting the teeth. With these appliances any man who can tend the brakes and set the log can keep the saw in order. The patents to W. B. Noyes bear dates March 8 and Aug. 8, 1868. Orders should be addressed to W. H. Hoag, sole agent for the United States, 314 Pearl street, P. 0. box 4,245, New York city. Baker & Noyes, manufacturers, Manchester, N. H. Interesting Experiment in Electricity The Boston Journal of Chemistry gives the following amusing and instructive experiment: " Procure four glass tumblers or common glazed teacups, and having wiped them dry as possible, hold them over the fire to evaporate any moisture which may still adhere to their surface; for if there is the least moisture it makes a connection and spoils the experiment. Place them upon-.the floor in a square, about one foot apart; place a piece of bod upon the tumblers, and have a person standing upon the board. This person is now completely insulated, the glass being a non-conductor of electricity. Now take a common rubber comb, and having wound a piece of silk around one end of it, rub it briskly through your hair, and draw the teeth parallel to the insulated persons knuckles, leaving a little space between the comb and the person's hand. The result will be a sharp, crackling noise, and if dark, there will be seen a succession of sparks. Repeat the process until the phenomena cease. The person is now "charged " with electricity, the.same as a Leydenjar. To draw off the electricity, approach your knuckles to the person's hands or his nose (being careful not to allow any portion of your body to come in contact with his), and there will be a loud snap and the sparks will be very brilliant. If a cat be held so that the charged person can place his knuckles in proximity with the animal's nose, it will suddenly appear as if it were in contact with an electric battery. A glass bottle may be used ia Beffoi'tfee eeml , but ft is not so well adapted for the" purpose. Much amusement may be derived from this extremely simple experiment, and some of our numerous young readers will hasten to try it for themselves." Improved Device for Adjusting Window Blinds If blinds to windows can be opened and closed in all weathers without raising the window, the device that enables this to be done is valuable. In winter, raising the window for this purpose, admitting the temperature of the frigid zones, even momentarily, is not pleasant; in summer, the consequent ad- mission of dust is annoying ; at any time or season, the danger of falling by leaning out of the window to fasten or unfasten the blind is not to be risked. Several devices for obviating these difficulties have been brought under our notice, and although we have found some good qualities in each, we havefoundno one so free from possible defects as that herewith illustrated. The engraving shows a device by which the blind may be opened or closed from the inside, and held in any position desired, either closed, fully open, or at any intermediate position, in all of which it will be securely locked. Attached to the frame of the blind is a rod upon which slides a sleeve pivoted to the outer end of an arm secured to the axis of a worm-gear seated in a recess in the window sill, and gradually rotated by a worm, the whole covered by a metallic plate, as seen, which may be made as ornamental by plating or japan- ning as may be desired. The worm, or screw, is turned by a shaft and an ornamental handle inside the ' room. As this handle is turned, the gear is slowly rotated, and its arm, sliding on the rod or bar, throws the blind back or forth, according to the direction of the rotary motion, opening or closing it as desired. In whatever position the blind is left it is immovable, except by having recourse tothehandle, or crank, inside the room. The device is capable of being made highly ornamental as well as useful, as may be se'en. Patented by Wm. B. Brooke, October 20, 1868. Rights for sale and samples to be seen at the office of G. L. Taylor, 88 West street, Trenton, N. J. The Safety of Steamships A correspondent, " An Engineer," writing to the Times, has hit the nail on the head, in so far as the clearance of water snipped by steamers in heavy weather is concerned. He proposes to lift the water from any part of the hold by means of steam j ets, supplied from the boiler. It is astonishing that this'simple application has not been before made. In the case of the Giffard injector, when feeding into a boiler under a pressure of 100 lbs. per inch, the water must be forced with an energy sufficient to raise it to a hightof at least 800 ft,, but in the case of a steamship, with water in her hold requiring to be lifted 20 ft. only, a steam jet would lift between forty and fifty times its own weight of water. Thus, in the case of a steam vessel having boilers capable of evaporating 1,000 cubic feet of water per hour, the steam taken from them and employed in jets would lift at least 1,000 tuns of water per hour from the hold. The same amount of steam employed to work centrifugal pumping engines would, of course, do very much more, but the steam jet system has the advantage of great simplicity. Arrangements should be made for applying it in all steamers. It would, almost beyond question, have saved the London and the Hibernia. The following is the principal portion of the letter under notice, addressed to the Times : " In the steamships London and Hibernia we had from 500 to 1,000-horse power of boilers, all in good order, and plenty of coals. In other words, we had from 500 to 1,000 horses all ready knd willing to work, all thoroughly under command, with plenty of food; and yet no harness for them; plenty of work for them to do, and nothing to do it with. " I think it was Count Rumford who said the boiler was the soul of the steam engine, and truly here the spirit was willing and the flesh was weak. " What is the best mode of utilizing all this power of work? It is not a question of economy of fuel, it is a question of life and death ; and, therefore, while the arrangements for applying the power to eject the water should be effective, they must also be simple, ready of application, and certain to work when wanted, and also detached from the engines (for it is easy to see that the engines of the Hibernia could not have worked without a fly-wheel). If we are to have this, we must look about us for something simpler than pumps, either centrifugal or reciprocating pumps. All these require machinery, and take up much rcfom, and may not be ready when wanted. What we should have is a direct application of the steam, either in the form of Savery's engine or in one of the many ways in which the steam jet is applied to raising water, feeding boilers, etc.; and by this means no machinery is needed, and the whole power of the boilers could be instantaneously applied. " There is a well-known application of the steam jet for raising ashes out of steamers, but which would equally well raise water. . It is simply an annular j et of steam round a six-inch pipe, which creates a vacuum and discharges the ashes through the pipe. "Eachapparatus requires about 5-horse power of steam to work them, and they would raise one thous and gallons of water per minute. They are simply six-inch pipes, standing vertically, and take up no more room than a stovepipe. They might be placed all round the side of the vessel by carrying a steam pipe to them, or they can be placed in any part of the ship. " Now, if there was 1,000-horse power of boiler, you could have 200 ejectors before the whole power was utilized ; but if there were only 26, 20,000 gallons, or about 120 cubic yards, of water would be raised per minute. By employing the whole power, 1,200 cubic yards of water would be ejected a minute.—Engineering. [The plan here proposed and advocated has, been tfsed in this country for many years. Ejecting bilge water, and even raising sunken ships when not at too great depth, can be readily done with a steam siphon.—EDS.