The Editors are not responsible for the Opinions expressed by their Correspondents. Single-acting Toy Steam Engine, Messes. Editobs.—The description of the toy steam engine, published with illustrations in No. 5, current volume of your valuable journal, was interesting to me, because I have one something similar which I "built as evenings' amusements while an apprentice. I think it is easier to make than the one you describe. The boiler head is a brass casting, A, of a triangular form, having a circular flange, B (dotted lines in Fig. 2), fitting into the boiler, C, which is of sheet copper or brass, spun from a single piece. The cylinder, D, oscillates on a screw, E, passing through the flange of the cylinder head, F, and the boiler head, and secured by a set nut, G, under the plate. The face of the flange of the cylinder head is held to the surface of the boiler head by a spiral spring under the head of the screw, as seen in Fig, 1, which is a side elevation or vertical section The piston is turned concave with a thin edge on the steam side, left slightly larger than the bore of the cylinder, and which may be spread with a burnisher when it leaks, thus forming a spring packing. The boiler has no gage cock, although one might be easily attached, and it is filled with water through a hole, H, Fig. 2, which may be plugged with a small screw. The leg at the wheel end is made of a tube through which the shaft of the wheel passes, its end resting on a step in a cross-piece, I, to receive which the pipe is split about half its length forming two feet. It will be seen that the wheel runs through a horizontal plane, being mounted on a vertical shaft Heat is applied under the boiler by a gas jet or a small spirit lamp. The joints are all made with hard solder. Holes in the wheel end of the cylinder admit the atmosphere for the return stroke. The machine is very simple and easily constructed. It is a source of great amusement, as it hums like a top. Daniel Davis, Jr. Princeton, Mass. Incrustations on Iron. Messes. Editobs:—I have just been reading in the Scientific Amebican the article on boiler incrustations. I have frequantly noticed in our kitehen an iron pot, smooth as glass on the inside, Wliich the old cook keeps forever over the burning coals, with boiling water; beside that stands the tea-kettle, also iron, but rough as a grater inside. Now, in the pot the water never deposits crust, nor is there any sign of it; but in the kettle you might almost build a brown-stone house with the incrustation if you could get it off. The idea occurred to me, that all boilers could bs made smooth inside (and you could not have them too smooth), they ought to be slippery as ice; or why not line thorn with porcelain as all our cooking utensils are, which are often over tremendous fires ? Let the inside only be smooth, and it. ap- pears water could not then incrust them. In our pump is sulphate of lime. Mbs. Edmund Pbatt. Bridesburg, Philadelphia, Pa. [Cast-iron cooking utensils are generally made of very hard iron. When of soft iron they are liable to corrode as well as to gather incrustations. The very hard iron will keep clean. It is obvious that such hard iron could not be used in making steam-boiler plates, for it could not be wrought, and would not have the requisite tenacity. The conditions of a culinary vessel and a steam generator are not the same. The temperature of the interior of a kitchen pot cannot rise much above the boiling point of water, 212 Fah., but that of the steam boiler not unfrequently rises to 365 Fah. —Eds. Rat-proof Buildings. Messes. Editobs.—I noticed an article from the American Buttd&r relative to the discomforts of the people of Chicago, occasioned by the vast number of rats whieh infest that city, and asking if any one can invent a. style of building which shall be rat proof. I have wondered many times, that the builders and proprietors of the grain elevators and large warehouses of the West have not ere this adopted the English plan of making their buildings rat proof. The same material, in a more finished state, is used for first class dwelling houses. If used by the people of Chicago, they will be free from the encroachments and destructiveness of rats,as well as the filth, bad odor, and the disagreeable gnawing sounds caused by them. The plan adopted in England is to have the floor of slate, sawed and planed to uniform sizes and thickness. The walls are also covered in the same manner with sawed and planed slats, well jointed and secured to the wall or studding with screws, which makes each room as secure against rats as an iron or stone box would be. The slate used for the floor is from one to two inches thick, and that forthe walls half an inch thick. For warehouses, elevators, and such buildings, it would be less expensive to use it as it comes from the saw and planer without being sand-rubbed; but for costly dwellings the slate for the walls is marbleized, by which process a perfect imitation can be made of any of the foreign marbles, rendering the rooms at once gorgeous and beautiful in appearance. The Vermont slate, which is of handsome light variegated colors, polished to a glossy surface, would appear finely and be preferred by many. But the imitations of light foreign marbles, such as Sienna, Lisbon, brocatelle, porphyry, and the like, would be richer and livelier in color, making the rooms more pleasant and light. The slate is wrought into different shapes and forms to suit the taste; some in panels, others to represent blocks of marble of one or of different colors. For plainer dwellings it may be used in its natural color without polish or extra finish. There is no doubt but that slate used in its plain form for the floors and walls of stores, mills, and elevators, and even houses, woiild render them rat as well as fire proot. I. I. W. Fairhaven, Vt. —— Crank Pins of Inside Connected Locomotives. Messes. Editobs:—I propounded the simple question, "Why the inside connected engine requires a crank pin so much larger than an outside connected one V and by way of answer a gentleman, who is a first rate mechanic, asks, "Why does the axle of a locomotive need to be larger than the crank pin ?" The crank pin and axle perform two different offices, and in the case.of the inside connected locomotive there is very little difference between the sizes of the two parts. I will answer my own question in this way : There is no need of the pin being any larger than for an outside connected engine, for it would break of any aize if exposed to the same influences. Since the crank shaft is one solid forging, and of the worst form to bear sudden shocks or jars, it seems to me that the frequent breaking of them is from natural causes; that is, sudden strains from the track, unrelieved by any spring or counterf orce. The action of the pistons, in addition to the sudden elevation of one side two inches or more from a plane, causes a very severe twist, which not unfrequently breaks the solid crank pin of six inches, while the four-inch pin (outside connected) escapes. The outside connected engine has no such strains to encounter in its crank pin, having merely to turn the wheel. I hope this is not " an evasive answer." Egbeet P. Watson. Do We Measure Horse Power Correctly ? Messes. Editoes :—When we wish to find the actual horse power of a steam engine, and compute the same by multiplying area of cylinder by stroke of piston, pounds of steam, and number of strokes per minute, imthout other qualification, the result is erroneous; as, for instance, apply the foregoing rule to a steam engine furnishing power for a machine shop, and running at the rate of saventy-five revolutions per minute, and let the result in horse power be thirty; then disconnect, throw the belting off the power wheel, use the same amount and pressure of steam, and the number ot revolutions will be doubled on account of outside resistance being removed. Mow, measure the horse power by same rule, and the result will be sixty-horse power, which is evidently absurd; for it is equal ta saying that the engine uses most horse power when doing least work, and least horse power when doing most work. It appears to me, that the actual horse power of an eagine,. is only and simply the amount of power throwjj off and made use of, and should be competent apart and distinct from the power consumed in the engine, per se, and I therefore beg to suggest the following rule for computing true horse power. Calculate, by present method, the horse power of any engine doing actual work, at any given number of revolutions, and then find the horse power consumed in producing the same number of revolutions when not doing any work; subtract the one from the other and the result will be the true horse power of the engine. To assist purchasers, it should be incumbent upon all build-ers of, and dealers in steam engines, to know the exact horse pjw6r consumed at any given velocity in any engine, perse, they may have for sale. It must be admitted that a better test of the superior economy of one man's make of engine over another, could scarcely be had than that of the amount of steam consumed in running any engine alone. New York city. Mathematician. m tm p Wonderful Results from Expanding Steam. Messes. Editoes :—A friend has handed me a pamphlet of 50 pages, elaborately illustrated, and said to have been extensively circulated, by a Steam Engine Company, who claim a capital of $200,000. In this pamphlet diagrams are given of cards, said to have been taken from some of the Company's engines while at work. As shown by these cards, their engines work in absolute defiance of the known laws of forces, and the men who circulate them evince a wonderful contempt lor the science of the age. To add still more interest to these curious diagrams, they are examined, commented upon, and greatly approved of, by a "Chief Engineer," "Inspector of Steam Boilers" in a certain Congressional District, and, as the Company assures us, " one of the most thoroughly informed engineers in the country." This surely gives them respectability. Now, if indeed this Company, with their " Chief Engineer," can set aside the laws that have heretofore governed the movement of forces—laws that the steam engine has always most obstinately refused to disregard—it is a curious fact which your readers should know, and with your permission, I will describe, for their consideration, one of these wonderful diagrams with a brief analysis. The one I select is said to have been taken from an engine 12x24 inches, making 90 revolutions per minute. We are not told at precisely what point the steam ports open; but as the exhaust line on the card is down near to the atmosphere until within 1 \ inches of the end of stroke, and there mounts almost perpendicular so as to reach 40 pounds at the end, it is evident the port is well open at the commence merit. The piston has scarcely moved forward when the pressure line reaches 60 pounds; which pressure is maintained exactly uniform for just 1 inches, where, we are informed, "the steam is cut off short" and expansion commences. When the piston has advanced 3 inches, and the steam expanded to just twice its volume, the pressure line is still up to 42. At 4J inches, three volumes, it is up to 82, and at six inches, having expanded to four volumes, it still maintains a pressure of 23 pounds. At the end of the stroke, when it has expanded to sixteen times its original volume, although the initiatory pressure was but 60 pounds by the gage, or 75 pounds all told, it still maintains an effective pressure of 3 pounds, or 18 pounds including atmosphere, and, as we are assured by the builders and the " Chief Engineer," it has given an average effective pressure of VX\ pounds for the whole length of the cylinder. Now, suppose this steam at 60 pounds, or really 75 pounds pressure, to have been a perfectly non-condensing gas, and to have been allowed to expand without resistance, say in a vacuum, to 16 times its volume, the pressure would be, 75-H 16=468 pounds, or about 10 pounds below the atmosphere. This is in accordance with the well-known law of the pressure and expansion of gases—a law deduced from the great principle of equilibrium which controls the movement of all forces, and is the very soul of mechanical science, and demonstrated by a thousand experiments. Every perfectly elastic fluid, when under pressure, possesses a power exactly equal to the product of its wlums and pressure. If the volume is 5 and the pressure 100, the power is 5 X100= 500. If allowedjto expand freely until the volume is doubled.the pressure will sink to one-half and we have, as the power, 10 X 50=500. If it expanded to 5 times the original volume, that is, 25, it must divide out its pressure equally between these five volumes, and can, of course, give to each but one-fifth of its original pressure, 20 pounds. We then will have 25 X 20 =-500, and so we may go on expanding to 100, or 1000, volumes with the same results so long as the expansion can go pn without resistance. But to assert that this gas can, by the act of expansion, multiply the power, so that the product of its volume and pressure will be greater after expansion than before, is to assert that power can be created by merely a mechanical movement—the old dream of perpetual motion— simple absurdity. But let us return to our diagram, and see just what our Steam Engine Company and their "Chief" do claim. Steam in cylinder before expansion, vol. 1, pres. 75; 1X75—75: after expansion, vol. 16, pres. 18; 16 X18—888. These results show a multiplication of power more than three times. This is monstrous; but all is not yet told. We are assured that the average effective pressure, that is, the work dona by this steam, was 17 pounds for the whole length of the cylinder. However, before proceeding to inquire into this question of the work done, we must return for a moment to the law of expansion. We have seen that the mere enlargement of a perfectly elastic gas is but a division of its pressure among the several volumes into which it has expanded; the whole mass containing the same amount of force, after, as before, the expansion. Now let us inquire what is the effect when this expansion occurs under difficulties. When the expanding gas meets with opposing forces, where it must move from the path heavy obstacles, and work its way to an enlarged volume at great cost, as steam expanding behind the resisting piston; does any one claim that all this resistance is removed without cost ? Can power be exerted without expending force? No more than (Jod can be false. Then for every pound raised, or moved, by the expansive force of steam, or any other gas, it must yield an equivalent, and fall just so much below its original power. Now as the measure of heat contained in steam, or gas, is the measure of its expansive force, and as heat and force, or motion, are equivalent, and when combined with an elastic fluid, are identical or convertible, it follows that in expending force, heat is lost. And it has boen found by careful experiment that for evijry 773. foot-pounds "of force exerted, a unit of heat—an amount of heat sufficient to raise a pound of water one degree in temperature—must be expended. Now in the case under consideration, we are told that the effective power obtained was equal to an average pressure of 17 pounds for the whole length of the cylinder. The initiatory pressure of 60 pounds for 1 inches would make for the whole but 3J pounds; then there remains 13 pounds to be supplied by expansion. This requires a force equal to 3,107 foot-pounds. Again, the atmospheric pressure of about 15 pounds must be pushed back by the expansion, and will require a force of 3,178 foot-pounds. These together amount to 8,235 foot-pounds, equal to eight units of heat; which is necessarily withdrawn from the steam. Lgt-3"se'e what this will leave. The amount of steam admitted to ths cylinder is 169J inches, the pressure 75 pounds. Steam at this pressure has a volume of 5'7 cubic feet per pound, and a total heat of 1,175, or units. As the steam admitted is but one fifty-eighth of a pound, it contains but twenty units of heat. We have seen that eight units have been expanded in the work done; we then have but twelve left in the expanded steam. How, I ask, in the name of all the philosophers, can saturated steam, at 75 pounds pressure, expand to 18 volumes against a resistance that will cost eight-twentieths of all its heat and still maintain a pressure of 18 pounds, when a perfect gas, starting with the same pressure expanded, without resistance, or loss of heat, to 16 volumes, will sink to 4-68 pounds. The whole thing is absurd. The days of miracles have passed. No such card was ever fairly taken from any steam engine. E. S. Wicexin. Keokuk, Iowa. [The writer of the above appears to reason and write " by book." His theory is right, but his assertion that the diagram to which he refers could not have been fairly taken from any engine, is not sustained by practice. We can show him many equally at variance with the theoretical diagram. One important point does not seem to enter into his calculation; that is what engineers call " clearance," which may be defined as all the space from the closing valve to the piston, when on the dead center, including the passage to the exhaust valve, which is a large percentage; in this case, by estimate, about one-twentieth of the whole cubical contents of the cylinder. Now the steam that fills this one-twentieth is not represented onthe theoretical diagram, and hence it would have to be added to the practical, or actual diagram, and would make the terminal expansion higher, say by three pounds. This does not, however, account for the whole of the discrepancy shown, and we must look for some additional cause. This is unfortunately, too common, and is occasioned by want of perfect workmanship. It is the leaking of the valves. This would, of course, keep the pressure of the expansion line above the theoretic line in proportion to the amount of steam admitted after the valve had closed over the port. A diagram represanting the clearance, and carried below the atmospheric line would have shown, clearer than we can do by words alone, our idea. We publish our correspondent's article and his diagram, however, as they form an excellent exposition of the theory of expansion.—Edb. For the Scientific American. Our Sun tbe Origin of all tbe Forces on Garth. When we trace backward the origin of all forces or motions on the surface of our planet, we come to the necessary conclusion, that they all, with the single exception of the ocean tides, are to be found in the heat of the sun. In fact, this heat causes air currents, and so -the force of the wind; it evaporates the water of oceans and lakes, which, coming down on mountains as rain, forms streams, and gives water power in its descent. Again, this heat of the sun causes plants to grow, which, storing up heat in their fibers, procure us a fuel, either fossil as coal, or recent as wood; which fuel, by its combustion, gives us only the heat of the sun back, which heat is thus made available to us at any place, at any time, and is also easily transformed into motion by means of steam or caloric engines. Or, again, the vegetable matter formed by the light and heat of the sun, is consumed by animals as food; and the stomach of animals acting in certain; respects like the furnace of a steam engine, sets partially the hidden heat free to keep the animal system at the proper temperature, and partially consumes this heat to produce muscular motion for moving the individual itself, and partially this muscular motion may be applied to produce motion of matter, overcoming all. kinds of resistances to this motion, and this last is what is commonly called force. The use of a number of pounds only, as a measure of a force, without referring to its motion, notwithstanding extensively applied, is, when critically examined, very erroneous; as is also the old definition of force as something which " can create or destroy motion of matter," alT if force was something exterior to matter and independent of it. Force, on the contrary, is the manifestation to us of something co-existent with and inseparable from matter; no force without matter, and, as far as our experience goes, no matter without force. Matter shows itself to us under different forms, and continually undergoes the most stupendous transformations by chemical and other agencies. Sometimes a light, invisible gas like hydrogen becomes condensed without any external pressure, in the one-thousandth part of its former space, in the metallic state in palladium, increasing the weight of this last metal almost one per cent; or this same gas combined with another gas, nitrogen, making the mysterious metal ammonium, forms a perfect amalgam with mercury, swelling its bulk till it becomes lighter than water, and will float on it. Similar transformations we observe in force : one time it willmanifest itself to our eyes as light streaming from the sun; then as an agent expanding matter, and giving to our bodies the sensation of heat; then changing the solidity of ice into the fluidity of water, and this again into the highly elastic vapors or steam—by every one of these molecular changes, a portion of heat disappearing, becoming latent, to reappear again when another change occurs in the opposite direction. By not only overpowering and destroying the natural cohesion of the waters molecules, but changing it in a powerful repulsion, this force increases the bulk of the water more than a thousand times, and enables it to exceed not only pressure, but to move heavy bodies; thus we may transform molecular force, or heat, into motion of the masses which then is distinctly observable to most of our senses. This constitutes what formerly, exclusively, was called a force, when heat was erroneously supposed to be some kind of imponderable fluid, having a separate existence, independent of matter. Thus tracing back all motion on earth (always excepting the ocean tides) to the magical power of the sunbeam, the next natural question is, When e this light and heat of the sun'/ This question, of all-absorbing interest, I will treat in a following article. P. H. Vandeb Wbyde, M. D.