Increasing Speed of Ships To the Editor of the Scientific American : Recently there has been much discussion in regard to the best methods of increasing the speed of ships. The old and standard way of applying more power, seems to have nearly reached its limit, when engines aggregating 70,000 horse-power are placed in a single hull. Doubling the amount of power adds but a small percentage to the speed. Skin friction is probably 75 per cent of the whole resistance to motion. Experiments point to a rapid increase in this element as the speed increases. Skin friction is a great obstacle to be overcome in building fast ships. The hydroplane is an effectual way of getting rid of it in small boats, but it requires a large horse-power for vessels of any considerable displacement, and as yet the hydroplane boats have not proved exactly seaworthy. Whether the system can be effectually applied to large tonnage appears to be a doubtful question. Its fundamental principle is the reduction of immersed, or wetted surface, and in this way getting down the skin friction. More than 35 years ago the writer, in conversation with a mechanical engineer, suggested compressed air as a lubricant for vessels. He was told in reply that the idea was not new. Years before a man had the idea of placing a perforated pipe on the stern of the vessel and carrying it down and some distance along the keel. Air was to be discharged from this pipe against the hull. The idea was to form a coating of air between the water and the skin. Upon experiment it was evident that the vessel went considerably faster when air was discharged through the pipe. The result was so promising that government experts were called and made careful tests. The horse-power required for the compressor, power of the main engine, the speed attained, and all the other items were carefully observed. The final results as observed at that time seemed to show that the horse-power saved was very nearly equal to that used in compressing the air. At that day there was nothing to be gained by the invention. It seems probable, however, that a different result would be attained to-day. Then almost nothing was known in regard to the economical compression of the air. Practically, the art of compression was not even in its infancy, for it did not exist. With modern machinery for supplying air, a very different result might be expected. It was an idea far ahead of its age. Those who remember something of the old-fashioned air pumps of compressors, built 35 or 40 years ago, would feel tolerably certain of being able to supply the outside of the ship with a film of air at a tenth of the cost of power used in the early experiments. It has been suggested that an oil film might be applied to the vessel' s hull to reduce the skin friction. Racing yachts, by using suitable bottom compounds, make a considerable gain in speed. Whether pot-leading can be automatically and continuously applied, is a question ' that might well be considered by inventors. Nature applies such a coating to fish and an imitation of Nature' s process does hot seem altogether impossible. W. E. De Pertreche. [Referring to the writer' s suggestion that 70,000 horse-power is the limit for ships, it should be noted that our new 35-knot battle-cruisers are to have at least 175,000 horse-power. Experimental tests- in the touring tank do not give promise of any economical reduction of friction through the use of an air film.-- EDITOR.] Unsinkable Ships To the Editor of the scientific American : In these days of destruction by means of torpedoes and' mines the question must often arise, whether it is possible to devise some method by which the effect of explosion, as applied to the bottoms of ships, might be modified, if not entirely counteracted. In the case of a vessel constructed with two bottoms with an air space between, the force of the explosion shatters the outer shell and is conveyed to the inner bottom which also suffers from the force of the confined gasses, to a less degree than the outer shell, but sufficiently to allow the influx of water and cause the sinking of the ship. If in the case of the Lusitania the Ancona the Ville de la Ciotat or the Persia the space between the two bottoms, instead of being an air space had been packed with a tough, fibrous, resilient substance, it is quite conceivable that one or other of the following conditions might have arisen : (a) The explosion would have shattered the outer hull, but the disruptive effects would have been neutralized by the resilience of the packing and the inner bottom would have remained intact, or (b) The force - would have exerted itself through the resilient matter to the extent of breaking the inner shell, but the expansion of the resilient substance, following its compression by the force, would have prevented, or at least retarded, the influx of water. Of course, these propositions depend upon (a) the energy of the explosion and (b) the resilience of the interposing material; but upon the presumption that the latter was sufficient to modify the former it appears to be self-evident that the sinking of the steamer might have been delayed if not prevented. The question is, Is it possible to find a material possessing the qualities of toughness, resilience, and (comparative) cheapness, that would have the effect of neutralizing, to a greater or less degree, the effect of high explosives as applied to the bottom of a ship ? After investigating a number of materials I have formed an opinion that scoured wool possesses those qualities in a marked degree and the theory I put forward, for others to test, is that if the double bottom of a steamer were packed with scoured wool, or other equally tough, fibrous, resilient material, it would be difficult, if not impossible, for that vessel to be sunk by explosives so rapidly as to prevent the saving of life and possibly also, of the ship herself. Louis E. Horne. "Hale House, Bishops Grove, Perth, W. A. [Judging from the press reports that have come from abroad, the above system has been applied in the monitors built for the British Navy since the beginning of the war.-- Editor.] Another Explanation To the Editor of the Scientific American : In your issue of September 9th an account is given of An Unusual Aurora, by Walter H. Eager, and the description tallies almost exactly with a phenomenon that is rather common at this place. The nebulous spots in the sky, as we observe them, are caused by the blast-furnaces which are located north of us and can be seen only during a certain condition of atmosphere. The blast furnaces are rather plentiful in this section and we observe that these luminous spots in the sky are always located in the exact direction of the furnaces. The shaft of light is.always vertical, and appears and disappears at irregular intervals, caused no doubt by certain vapors floating in the air over the stacks of the furnaces. It is likely too that the light shown in the sky is refracted at certain definite angles, similar to the rainbow. It is my opinion that the light originates in the heat or fires at hot-blast stoves of the furnace, and is projected into the sky through the smoke-stack in the form of a vertical shaft. It is likely too that- these illuminations could be faintly seen for great distances. -We can see them very distinctly here, from furnaces 20 miles distant. Elmer Habbold. Leetonia, O. More on the Chemical Barometer To the Editor of the Scientific American : Mr. S. Leonard Bastin' s article, Curious Hygrometers and Barometers, published in your issue of September 16th, informs us that the chemical barometer was invented by the meteorologist Admiral Fitzgerald." Perhaps not many readers will recognize under this novel disguise the versatile British hydrographer and meteorologist Vice-Admiral Robert FitzRoy-- the same who commanded the Beagle in the famous voyage in which Darwin participated. But FitzRoy did not invent the chemical barometer (also known as the storm glass, camphor barometer, camphor-glass, chemical thermoscope, chemical weather-glass, and paroscope ), and in his Weather Book, p. 443, he declares that the device had been in use more than a century before his time. His name has been connected with this scientific toy because of his belief that its indications were actually controlled in some way by the electrical state of the atmosphere. Mr. Bastin will find the history of the chemical barometer fully set forth in Dr. C. Kassner' s article, Das chemische Wetterglas oder Paroskop, published in Naturwissenschaftliche Wochenschrift, October 18th, 1908. C. FlTZHUGH TALMAN. Washington, D. C. A Boon for Autoists To the Editor of the SCIENTIFIC American: It has been my misfortune in the past six years to be in communities where the commercial lighting companies did not use electric trucks in their service, but had this been otherwise it has long been my plan to interest them in a magnetic drag attached to the rear of their trucks to gather the enormous quantities of steel particles that litter our paved streets and highways, doing thousands of dollars damage annually to automobile tires and draft animals. It is my purpose in this bit of correspondence to give to any public spirited firm using electric vehicles this idea, which could be developed with very little expense and operated at a very low cost, and the data it would furnish would be very valuable in many directions. Again, I have no doubt that any local automobile club or society would gladly meet the operating expense attached to such an arrangement, and this without a great deal of urging. Yours Respectfully G. H. Peifer. The Naval Bill To the Editor of the Scientific American : Allow an old reader, who has not missed reading a number for more than 30 years, to make a comment upon our Naval matters. The bill just passed by Congress is, at last, an answer to what your paper has been calling for all these years, viz. : a Navy bordering on our needs. It is the greatest vindication of your editorials that has yet happened, and I wish to have the Scientific American receive some measure of appreciation at least for its great work in that direction. H. E. Carpenter. Los Angeles, Cal. The Current Supplement IT is said that everything imaginable can be found in New York, and tucked away in corners of the big city are many little shops where the most unexpected things are made and where the most unusual occupations are carried on. In the scientific American Supplement No. 2129, October 21st, a short account of one of these shops is given in One of the Curious Trades of New York, which is accompanied by a number of excellent photographs. At the recent meeting of the British Association for the Advancement of Science the ' president made an address on New Archaelogical Lights, the important portions of which appear in this issue of the Supplement. Determining the Age of Blazes is an interesting bit of forest lore, accompanied by a series of instructive illustrations. Dynamic Balance of Machines discusses a matter of considerable importance where fast running machinery is in question. Hydrogen for Military Purposes gives facts relating to the production of this gas, which is required in great quantities for the inflation of airships and military balloons. Optical Stress Analysis gives a very interesting description of a method by which a number of important engineering problems may be investigated. The article is illustrated by engravings and diagrams, Armor Plate gives a very excellent history of the development of this material, and a brief description of its manufacture, written for the untechnical reader. This number also includes On the Suggested Mutual Repulsion of Fraunhofer Lines, Bacterized Peat and other topics of interest. Relation Between Carbon Content and Welding Qualities of Steel THE poor workman blames his tools; the good workman assures himself beforehand, not merely that his tool is in good shape, but that it is suited for the end in view. Among other items which he must take into consideration is the matter of carbon content. He may well be guided, in doing this, by the following table: Carbon content. Characteristic .. Remarks. 1.58............Will not weld ... Seldom used. 1.38............Will weld.......Used for hard tools. 1.12............Welds fairly ....Used for chisels, etc. 0.88 to 0.62.....Welds easily Used for files, etc. 0.62 to 0.38.....Welds readily... Used for rails and tires. 0.38 to 0.15.....Will not temper. Used for boiler plate. 0.15 to 0.05.....Will not temper. Substitute for iron. In choosing steel for any purpose it is' clear that the information afforded by this table is of value. Thus a crowbar of 1.58 per cent carbon steel, however carefully tempered, would be inferior to one of 0.88 per cent carbon steel, reasonably well tempered. The former would be brittle compared with the latter. Likewise the content of phosphorus and silicon is of significance. It may be estimated that the effects of phosphorus, carbon and silicon in hardening steel and making it less capable of resisting blows are about in the proportions of 3:2 :1. Killing Germs Electrically ARECENTLY passed Federal law requires a system of drinking water purification to be used on public carriers. An equipment using ultra-violet rays from a mercury vacuum light has proved successful for this work and is being installed on many of the large lake passenger boats. A mercury tube is immersed in a tank or receiver in the water system so that all the water used is at one time or another exposed to the ultra-violet rays from the tube. Inasmuch as the mercury tubes require 220 volts, direct current, and the lake boats have but 115 volts available, motor generator sets must be provided to operate on 115 volts and provide 220 volts for the lamps. The operation is automatic; if the tubes burn out or the voltage fails, the electrically controlled intake valve of the tank is closed. This is undoubtedly the first time a motor generator set has been used to kill germs.Making Biological Specimens Transparent AGLASS of cracked Ice Is quite opaque. But if water be poured in to fill the interstices between the fragments of ice, the combination becomes mildly transparent Why? The answer is a simple one. The refraction index of ice is different from that of air. Ice is far from opaque, air is wholly transparent; but in passing through either medium light suffers certain refractions. If we attempt to pass it through a considerable number of alternate thicknesses of ice and air, the combined successive refractions disrupt the light waves completely, and none survives the passage. But if for the air we substitute water, of substantially the same refractive index as the ice, the effect approximates that of a single homogeneous medium, and the light passes through with substantially the simple refraction which it would suffer from such a medium. Dr. Spolterholtz, of the University of Leipzig, whose major interest lies in the technique of the preparation of biological specimens, recalling the principle on which this induced transparency rests, asked himself whether he could not apply it in his field. He argued that where an ordinary specimen exhibits but one feature of an animal' s structure, if all the tissues could be made moderately transparent, a single specimen would suffice to exhibit the entire anatomy of a species, and would show the inter-organic relations in a graphic manner never before possible. The proposition is not so wild as it seems. Organic matter is far from inherently opaque. There was good ground for the learned doctor to hope that he might resolve the apparent opacity of animal tissues into a matter of refractions, and by some means Introduce sufficient homogeneity to apply the analogy of the glass of ice and water. So he attacked the problem with this point of view, and by its solution has established a new school of specimen preservation which has already attained the most startling results. The method is simplicity itself. The organism to be preserved is treated to a preliminary dehydration similar to that employed for microscope specimens, followed by deflation with an air pump. It is then impregnated with and immersed in a liquid whose refractive index is equal to the average index of the solid matter. At first carbon disulphide was employed for this purpose, mixed with other liquids to afford an adjustable refraction index. This substance is ex plosive, however; so it has been abandoned in favor of a mixture of methyl ether, salicylic acid, and benzyl benzoate. By varying the proportions of this simple mixture a range of refraction index is obtained quite equal to that of the organisms to be embalmed. Circular containers are out of the question because of the refraction from the curved surface. Rectangular jars are made of a special glass of variable index, fixed in each case to correspond with that of the contents. These are held in place by suitable supports, and a small air space is left beneath the sealed cover to care for expansion. The results are extraordinary. Our engravings, while not fully indicating all the shades and tints of the originals, at least give an idea of the degree of transparency. In the case of the mouse it is especially clear that all the creature' s internal dispositions are distinctly visible. It goes without saying that these specimens are far ahead of anything previously developed. Entire human arms and legs are put up by this process, and become clearly transparent, the far side being as distinct as the near one; and at last accounts a jar was being planned to hold an adult human body. The arterial and nervous systems are differentiated by the injection of red and blue fluids of appropriate refraction index; and efforts are under way to develop a workable injection to mark out the nervous system. At the present time these specimens, like all other articles . made in Germany, are unobtainable here; but the end of the war will doubtless find them still a feature of the German scientific workshops, so that we may expect them to be then available. Boston' s Care of School Children' s Teeth IT NLIKE the medical -practitioner, the dentist re' quires a complex equipment in order that he may work effectively. The multiplication of isolated dental units necessitates the duplication of many parts outside the chairs and the instruments of general application. Moreover, no form of professional activity offers more opportunities for the transmission of disease from one patient to another; hence the most rigid asepsis is an essential of dental work. A central plant, where the sterilization of every thing that enters a mouth is under the control of an individual whose sole business this is, furnishes a more complete check on infection than the most conscientious divided effort in a multiplicity of small plants can possibly achieve. Then, too, while the physician who devotes two or three hours per day to a public charity feels the income loss slightly if at all, having a large part of the day in which to recoup the time thus spent, the busy dentist who gives of his daylight hours to a charity must take from this a definite loss of income which he cannot make up. On all these grounds a large endowed central dental infirmary is vastly to be preferred to the distribution among hospitals and private dentists of the work which such an organization would properly undertake. A very interesting foundation of this sort is now under way in Boston. The Forsyth Dental Infirmary for Children is a charity incorporated under the laws of Massachusetts for the purpose of furnishing to the worthy children of Boston that dental care which is more and more being recognized as a fundamental prerequisite of proper physical condition and good mental. effort. Its first group of Trustees was made up of leading educators and professional men, together with three competent dentists. The Infirmary has set itself the task of caring for mouth conditions in children under the age of sixteen. The problem is a large one. About sixty per cent of all school children who are submitted to examination are found to possess defects originating about the mouth, including improper nasal breathing, hypertro-phied tonsils, and defective teeth, palate and cervical glands. The trustees of the Forsyth Infirmary have given deep thought to the matter, and have concluded that oh all grounds it is wiser and more practicable to bring the children to the dentist than to bring the dentist to the children. The child' s time does not begin to be worth as much as the dentist' s; and the element of time apparently lost to education can really be ignored, since it is repaid many times in the ultimate outcome. So the work of the Infirmary was inaugurated by the establishment of a large central dental workshop, in a building constructed for the purpose. At present the equipment comprises sixty-four chairs; but early