[THE editors are not responsible for statements made in tfee correspondence column. Anonymous communications cannot be considered, but the names of correspondents will be withheld when so desired.] Wanted: A Humane Animal Trap To the Editor of the Scientific American: The Massachusetts Society for the Prevention of Cruelty to Animals, Boston, has just published a pamphlet setting forth in text and illustrations the cruelties of trapping wild animals, such as foxes, etc., for their fur, by means of the old-fashioned steel trap, and the inhumanity of the thing is so vividly portrayed by both pen and picture, that I appeal to- the ingenious readers of your extensively circulated paper to put their minds to work to devise a humane method of catching these animals, if they must be caught, and to put an end to the horrible torture-dealing steel trap of the centuries. To better understand the subject, I would suggest that your readers write the above-named society for a copy of the pamphlet, which will be sent free of charge, so that they may see and understand from the illustrations what furs cost in torture of wild animals, which have the same right to a painless and merciful death that our domestic animals have. There is a great opportunity for some reader of the Scientific American to not only win ' for himself the thanks and the gratitude of humane people the world over, but also a more substantial reward in dollars and cents, by inventing a humane method of capturing these animals without first crucifying them. Brooklyn, N. Y. George Foster Howell. The Maximum Parcel Post Package To the Editor of the Scientific American: Mr. Taylor's communication, published in your number of July 19th, page 51, on The Maximum Parcel, is very interesting and highly ingenious. Allow me to observe, however, that no person has any serious doubts as to what is meant by length, although some may evidently differ as to the proper wording of a definition for the term. The definition of length as the greatest distance in a straight line between the two ends of the parcel is not as faulty as Mr. Taylor makes it appear. The ends of my rectangular receptacle, for instance, are two parallel planes and these are equidistant at all points, so that distance between the two ends cannot mean distance between two of the eight corners, selected so as to measure at an inclination to the length dimension of the package. The obvious reason for saying greatest distance in a straight line is to cover irregular packages, having no well defined dimensions, and to prevent too long a measurement by bending of the string or tape. As I construe the rules of measurement, the length of a parcel, however irregular such parcel may be, is equal to the length of the smallest circumscribed rectangular parallelopipedon, but this would be a dangerous definition to use as, some of our well fed country postmasters are subject to apoplexy, and you will find that it is difficult to say the equivalent of this school room definition in a few simple words. Arlington, Va. Joseph Becker. Progress in Air Navigation To the Editor of the Scientific American: Several recent visifs to Hempstead Plains have confirmed a previous feeling of disappointment, that the art of flying is still in the amateur, or bicycle staie. The automobile stage or practical application of the great discovery seems not only not in sight, but not even suggested. Langley's experiments (Smithsonian contributions, 1891-1893), showed that he had solved the problem except for three elements, all of which have since been supplied. First, a lighter and more powerful engine. Second, a method of safely leaving the ground and alighting. Third, a method of controlling the course of the aeroplane. (See Hiram Maxim, Century Magazine, January, 1895). . Three things strike the observer, on examining the latest machines now shown to the public. 1. Starting the engines by twirling the propellers. This .eejitainly seems primitive. Imagine it done under fire in warfare! 2. The fastening of the wings by wires, wire cords and flat strips of steel. These are fastened often by simply twisting through eyelets, or over pins, sometimes slightly soldered. Many of the recent fatal accidents are reported caused by the collapse of a plane. When it is considWei how the entire equilibrium depends on a few wire brti>l3ie trivial way in which these are fastened and mXIMTilllit, explains, to my mind, the ominous iiesrtlrllll, 3. The shri iiise-over rough ground must set up a. strain on the ' wire", and fastenings. It seems the extreme of careless management to subject all these slight bits of steel to the jarring and jolting caused by the great leverage of the long outlying planes and ailerons. A large space like a dance hall could be planked over, and the start and landing made with much greater smoothness. The wonderful ease and grace of the planes, once in the air; the speed, guidance and control; the floating and gliding return to the ground; all these prove that the main difficulties were solved two or three years ago. Since that time, there has been little gain, as far as can be seen, in the directions of wider use or greater safety. A model was shown last winter, in a Broadway window, of a platform hung beneath an extended plane, bringing the center of gravity lower. It would apparently hold a crew of eight or ten. The prospectus stated that it would come to the ground in safety, on the parachute principle, if the engines become disabled. Here is a suggestion of development which seems on right lines; as superior to the machines at Hempstead as the autobus is to the motor cycle. J. D. Holmes. New York city. [The progress that has been made in aerodynamics during the last two years has not been journalistically sensational. Hence, is not so widely known as it ought to be. Engine powers on the whole have been reduced and speeds have increased, proof enough that the problem of air resistance and of securing streamline forms has not been neglected. Eiffel's experiments, painstakingly conducted, for many years, but unheralded in the daily press, have disproved much of what was regarded as aeroplane gospel three years ago, and have enabled aeroplane designers to work more intelligently. Even some of Langley's work may be regarded as superseded by that of Eiffel. As for the minor points to which our correspondent calls attention, we might mention that more or less successful attempts have already been made to start aeroplane engines with cranks; that the wire fastening of the wings is not regarded by designers as the best method of stiffening a wing; and that some designers, notably Gallaudet, have very ably solved the problem of holding wings by other means. The difficulty of starting over rough ground is not likely to be overcome by the means proposed. If a large space like a dance hall, carefully planked over, is to be the chief reliance of the aeroplane in starting, why not recur at once to the old Wright starting rail, which is much simpler and cheaper? The truth is that an aeroplane must be designed to withstand the racking strains set up by bowling over rough ground at high speed. Dance hall platforms could never be ubiquitous. Indeed, the French military authorities realize this, and even require machines to run over freshly plowed fields and stubble. It is easier to adapt the machine to the ground than the ground to the machine.--E ditor.] Teaching the Tropics How to Live To the Editor of the Scientific American: In the issue of November 9th, 1912. of the Scientific American, we find a description in concise form of the application and maintenance of hygienic conditions in the Panama Canal district, to combat malaria, the greatest enemy of the white man in many tropical, subtropical, and some northern districts. But for these precautions and their results, it would have been far more difficult to achieve so great a success in such short time as was the case with the great Panama Canal. The afore-mentioned article clearly shows that such measures involve an extremely large expenditure. The statistics were derived from results obtained with only a part of the workmen employed on the canal, as some men were not made subject to these measures and others were beyond control because they cured themselves when stricken. The improved hygienic conditions tend to increase the number of working days, consequently a considerable sum of the working expense is saved, the wages being very high. The sum expended on hygiene will be cov-erad by the extra labor gained and the resulting increased output. Persons who have been employed in the tropics under quite different circumstances, for instance, in work on a smaller scale, with limited working capital, lower wages, and remote situation, are inclined to think that the costly method of conducting malaria hygiene is inapplicable in the vast majority of cases. I therefore want to point out in this letter how, on the Guiana placer in Dutch Guiana, a notorious malaria district at 120 kilometers from the coast, a really good result was obtained with very simple means and little outlay, but without prophylactic medicaments. This result was accomplished with 12 to 18 Europeans of pure European descent, most of whom came directly from Europe. The state of health of colored and white men who suffered a gIleat deal from malaria previous to their coming under the protection of these hygienic measures, was steadily improving, although recidivists were still occasionally absent through illness, especially when the hot season had just set in. For several years malaria has no longer been dreaded by Europeans on this placer, as there were no reports of absence through malaria in all this time. A detailed description of these measures is contained in my book, A Brief Outline of the Surinam Gold Industry, Geology, Technique, Hygiene, De Bussy, Amsterdam, 1911 (English edition). It will suffice to state here that I started upon the principle that in a country where the hygienic conditions are entirely different from those of a civilized European country, the mode of living should likewise be altered altogether, and not in some details only. The application and maintenance of hygienic conditions is not so difficult in itself, but the fact that it extends over a number of people, many of whom are careless by nature, does not facilitate matters. One has to exert will power, not only upon himself, but over others as well, and this in a popular manner. For medical and practical reasons, chemical prophylaxis is not suitable for a prolonged residence. In this instance the so-called mechanical prophylaxis is applied, the results of which are pronounced to be ideal. Our precautions did not extend bevond the actual dwelling place, because tha surroundings were exceedingly unfavorable for malaria hygiene. Owing to numerous swamps (drowned forest ground) and work pits, drainage or constant supervision would either have become very expensive or would have been altogether insufficient. A removal of the whole body of workmen and their dwellings to a more favorable situation at Savannah, some 5 kilometers distant, would have been both expensive and impracticable, because of the great distance of the places where they have to work. Only. the immediate vicinity was kept clean and in good condition. The houses were built in such a way that they were permanently airy; the light could come in freely, and the whole building was kept practically anophele free. Domestic work of any kind was done under gauze protection. The beds were provided with curtains of a special construction, which guaranteed the sleeper absolute safety from those anopheles which might accidentally have been indoors. The houses were connected with each other by means of a long passage, likewise provided with gauze. Supper was taken at six o'clock instead of at half past seven. After sunset few wished to leave these airy homes, although a pleasant recreation hall within safe reach drew many of the people to intercourse on account of the billiard and reading tables. The work-place was lighted by strong lights in case of night work; the surroundings were cleaned, and rest was taken in anopheles-free apartments. Another successful measure was based on the principle that the staff should have a certain interest in the strict upholding of the simple hygienic laws and the proper keeping of the hygienic arrangements. This was done by the superiors, who set the example by giving the staff instructions about the causes of illness and how to combat disease. Also a special wage system was introduced. This system was based on the principle that every good and careful workman is enabled to earn a very good wage, whereas in the case of malaria or sexual diseases the men had free nursing, but were paid only a small part of their ordinary wage; in the case of any other illness they received better pay. Then there was a premium paid for anopheles specimens caught indoors. The result was that everybody watched the results with the greatest interest and enthusiasm. The cost of our malaria hygiene amounted to the sum paid in the shape of surplus wages and salaries--in reality nothing but a health premium--and the expenditure for the installation of the gauze walls, windows, and doors of the buildings. Medical attendance for malaria cost us next to nothing. By laying down these rules, work on the Guiana placer was continued undisturbed. The adapted . mode of living and the facts that the hygienic conditions and the diseases prevailing in the country are generally knowr, and that the whole of the staff was made responsible for the proper order of affairs on the placer, combined to create for our men more agreeable work, and the company reaped the benefits of steady, undisturbed work. Amsterdam. Dr. J. H. Verloop. A Needed Plumbing Improvement.--A plumbers' supply man tells us of difficulties experienced in the use of the flushometer valve employed in lieu of flushing tanks. One difficulty results from fluctuations of pressure in the water supply which naturally varies the amount of water discharged at each flushing. The problem is to provide some means to overcome or counteract the effects of variation of pressure in connection with the present type of flushometer valves; or to devise a type of flushometer valve that will not be influenced by the pressure fluctuating in the water supply, but will deliver the desired amount of water at each flushing operation, regardless of the service pipe pressure.