The Metric Question--Both Sides To the Editor of the SCIENTIFIC AMERICAN : I have read with much interest the articles on the metric system by Messrs. Holst, Stewart and Kapeto in your impression for August 30. Taking up, first, the letter of Mr. Holst, I can imagine nothing more useless in the affairs of everyday life than the fact that a liter of- water weighs a kilogram. In the one field in which it might be of some use--naval architecture--it fails because of the increased gravity of sea water. It is not as well known as it should be that the assumed relationships of the metric units are only approximate. As Dr. J. W. Redway has put it: "The meter is assumed to be the ten-millionth part of the earth's quadrant ; but it is not. It is likewise assumed that the earth is an oblate spheroid, but it is not. It is assumed that the standard meter rod exactly repre-sents the calculated meter, but it does not. It is assumed that the kilogram is the exact weight of a cubic decimeter of water under given conditions, but it is not The liter is assumed to be a cubic decimeter, but it is not. Not one base unit of this 'scientific' system conforms to definition." Mr. Stewart may dismiss his fears regarding the decimalization of the inch. Here and there someone can be found who favors it, but it is not the program of the organized opposition to the metric system. The substitution of decimal for binary divisions of the inch would destroy existing standards as completely as the adoption of the metric system. Moreover, we regard the binary as intrinsically superior to decimal divisions for constructive purposes. Mr. Kapeto has explained this so well that I do not need to repeat it. Binary divisions are, in fact, as physical things, one of the few perfect things in this world. Unfortunately, they are awkwardly expressed by decimal arithmetic, but that is the fault of the arithmetic and not of the sizes. Everybody knows that choice of 10 as a basis for notation was a matter of accident and most unfortunate. Had those ancient races which originated the decimal system omitted their thumbs when counting, the metric system would never have been heard of. If we are to do away with something, why does no one ever suggest that we do away with decimals and adopt a more convenient base of numeration? It is gratifying to know that Mr. Stewart recognizes that "a certain loss to business nen is unavoidable," but he fails to recognize the chief loss. The couplings with which the hose ends of railway-car air brakes are connected were standardized, that is, made interchangeable, many years ago at the works of a leading manufacturing company. Because of that standardization, railway cars, both passenger and freight, when fitted with air brakes may be made up in trains regardless of the railroads of their origin and transported throughout our country. What would be thought of a man who would estimate the value of those standardized couplings in terms of the cost of the special tools and measuring instruments with which they are made? Is it not perfectly clear that their real value lies in the results which they accomplish, that is, the possibility of interchanging cars between railroads? As another illustration, consider standardized pipe-fittings. Because those fittings are standardized, they are made by the million and may be bought at trifling cost in any pipe fitting shop. The piping of a building consists of little more than cutting pipe to length, threading its ends with standardized dies and assembling the resulting pipes with their connections and fittings. Consider the conditions that would obtain when piping a building for steam, water and gas were it nece"ssary to make each fitting for its place and to order, and then ask yourselves what part of the real value of standardized pipe fittings is represented by the cost of the taps and dies with which the threads upon the pipe and fittings are made. Additional examples could be given without number, but these two should be sufficient to show that the value of these standards lies in the results which they accomplish and not in the tools with whioh they are produced. We make laborious--almost infinite--efforts to standardize mechanical constructions, and when the work is done the standards work so smoothly and accomplish their objects so perfectly that we almost forget their existence. Because of this a few well meaning gentlemen deliberately propose that we abandon these standards, begin afresh and place ourselves exactly upon a level with metric countries which have no structural standards worth mentioning. F. A. HALSEY. New York. To the Editor of the SCIENTIFIC AMERICAN : The letter from Mr. M. Metlin of Chicago appearing in your issue of August 16th shows the advantages of metric weights and measures for the measurement of length. They, however, are found to be even more convenient than there indicated. Americans have not only used decimal currency but have used it in the most convenient way. We do not say, for instance, that a coat costs 2 eagles, 2 dollars, 7 dimes, oand 5 cents, but we say that it costs $22.75. Metric weights and measures should be applied to each trade and industry in the most convenient manner, keeping the convenience of others in view. Last year the writer asked a doctor in the Sloane Hospital the length of his son who had recently arrived there. The doctor turned to the record and said, "154 centimeters." The doctor went on to explain that there and at other hospitals in America physical measurements had always been made and recorded in centimeters. Among the advantages of using this measure are that no fractions are required and that it is understood and used throughout the world. This is an instance of international standardization on the right basis. Now as our object is to do work most effectively we only follow common sense and good practice when we use centimeters to measure people even after they have passed 100 centimeters in height. It is entirely unnecessary to introduce the decimal point here. When 100 cm. has been passed the person's height is, for instance, recorded as 105 cm., 154 cm., or 180 an. The physical measurement of the students at Columbia University, for instance, is taken entirely in centimeters. If the new student is not familiar with centimeters, he is given a table of equivalents or told, for example, that 5 feet 8% inches is equal to 174 cm. H. RICHARDS, JR. New York. Visible Shells To the Editor of the SCIENTIFIC AMERICAN : Your Issue of August 2nd publishes a letter from Robert E. Womsley regarding visible shells in which he states that he never saw an enemy shell in flight nor anyone else who has. I know of course that it was not a common experience to see shells in flight but I did hear of several cases while in France so that my own experience in that respect was not unique. It was while we were stationed in the Ypres salient on a bright clear day in August, 1916, that the following incident occurred. I was on duty in a bombing post several hundred yards in front of our lines. Fritz was shelling our front line some 200 yards in the rear with a battery of apparently 5.9 H. explosives. The whine of the shells of course could be distinctly heard and happening to look up I saw the shells passing overhead apparently at a height of about 20 feet I counted at least twenty shells passing before the battery quit firing and could see as many as three in the air at a time. They looked like long lead pencils with indistinct blurred edges. Personally I am of the opinion that it would be impossible to see a shell in time to dodge it and the difficulty about hearing them is that although they may be heard distinctly enough a person could not judge the direction accurately within thirty yards or more. G. H. CLABK. Edmonton, Alberta. A Forerunner of the Salvaging Submarine To the Editor of the SCIENTIFIC AMERICAN : Your article in the August 16th SCIENTIFIC AMERICAN entitled "A Salvaging Submarine" puts me in mind of a similar apparatus used for raising the Swedish steamer "Rhea," sunk in 197 feet of water outside Stockholm in 1896 or thereabout. It was decided to lift the boat with pontoons and chains fastened in the portholes. To get the chain-hooks in the portholes, the depth being too great for divers, a 200-foot-long steel tube with a closed working chamber at the lower end was sunk in upright position alongside the vessel. The working chamber had a plate glass window and two arms or fingers on the outside which could be operated from the inside. The chain hook was guided into the porthole by means of these arms. When a sufficient number of chains were attached the vessel was lifted in the usual way. As far as I know this is the first and only time such a tube was used and I also believe this is the greatest depth, 197 feet, from which a vessel was ever raised. J. C. BJORKBOM. Reading, Pa. Some Blasting Technicalities To the Editor of the SCIENTIFIC AMERICAN : In an article on "Explosives" in the Mining and Scientific Press of Feb. 22, 1919, by Robt. S. Lewis, he says : "Fuse powder is a finely divided granulated 140 to 100 mesh black powder having potassium nitrate as an oxidizing agent. ... A good black powder should be of even grain, of suitable hardness and density and free from dust; and ten grains flashed on a copper plate should leave no bead or residue." In last week's- SCIENTIFIC AMERICAN, giving an account of the first "shooting" of oil wells with black powder, it says: "and the force of the explosion is always up the hole, following the lines of least resistance." With these facts confronting us, that in the explosive action of black powder, the bursting molecules of nitrogen gas escape up and out rather than down, we have a fundamental reason why misfired caps show burnt carbon on the cap surface, and that insufficient heat coming through the fuse, meets the compressed air always plugged into the cap by the close fitting fuse, and the instantaneous condensation of moisture results. Samples of fired caps will show extreme differentiation in the end spit of the fuse, and any brand of fuse tested by firing and holding the end of the fuse lightly on a smooth surface will show this woeful lack of natural precision. The remedy for this state of affairs, in the present method of handling fuse and blasting caps, is in supplementing a pinch of fuse powder between the cap surface and fuse end. Some one has said : "Any invention that tends toward eliminating the white man's burden, is a modern necessity." The manufacturers of these supplies and others interested, can never get anywhere shifting the blame upon the user and the fuse. The conclusion then, is this--that no one is to blame who has been careful with the best stock procurable, and still has misfires, and that such misfires occur: 1. By the explosive action of black powder following the lines of least resistance, and leaving too little powder at the point of contact--the cap surface. 2. Since the cap plugged in with the fuse does not constitute a vacuum, in the motion following the spitting fuse, there must necessarily be an equalization of the potential in atmospheric conditions. At such times when the fire in the fuse is not strong enough to overcome the air in the cap, the inevitable result is certain in the formation of carbon dioxide. Then, the unex-ploded cap is ready for its inefficient mission, if not worse. Standardized safety fuse lengths supplied by the manufacturers show the logical way out. These lengths should come to the user in paraffined cardboard cylinders. The caps on these fuse lengths should be guaranteed to the user--to explode, and with a suitable waterproof electric spitter for ignition. A. J. AVERELL. Medford, Oregon. A Poison Epidemic Among Wild Fowl WE have become so accustomed to ascribing disease to various germs or organisms, that we may be disposed at times to overlook other possible sources of epidemics. A curious instance in point is reported from Utah, where the annual losses from disease among wild fowl in the Salt Lake valley become so great that the Biological Survey undertook an investigation of the causes. Somewhat similar conditions have been observed on certain lakes of California, Cregon, Montana and Kansas. The birds affected with the disease become paralyzed, first losing their power to fly, and ultimately becoming entirely helpless. The investigation of the Biological Furvey has established the fact that the disease is due to a poisonous action of certain salts (calcium and magr-tsium chlorides) which the birds take into' their systerrs y\hen feeding in water heavily charged with them. uch concentrated waters occur on the drying fiats about the margin of Great Salt Lake, for example. With the cause, the cure also is found. The birds, unless too far gone, recover when given a good supply of fresh water. This is a simple remedy when dealing with individuals, but it is not so easy to alleviate the general condition which depends on local circumstances. A system of draining the land and increasing the inflow of fresh water is what is needed.