April 12, i88g.] 



SCIENCE. 



289 



countries, while the second contains samples of all the articles 

 which are manufactured in Belgium. A library and an information 

 bureau are attached to this museum. 



LETTERS TO THE EDITOR. 



*^*Correspondejits are requested to be as brief as possible. The ■writer's name is 

 in all cases required as proof of f^ood faith. 



The editor ivill be glad to publish any queries consonant with the character of 

 the journal. 



Twenty copies of the number containing his communication will be furnishea 

 free to any correspondent on request. 



The Robinson Anemometer. 



So long as the anemometer law is purely empirical, it is doubt- 

 less largely a matter of individual taste that one should prefer to 

 use a series of ratios whose values, even within the limits of or- 

 dinary usage, range between infinity on one hand, and 2.89 on the 

 other, — a value which corresponds, according to Science of March 

 22 (p. 227), to a wind-movement of 25 miles per hour. Neverthe- 

 less occasion may be taken at some future time to point out a 

 possible error into which one is easily led by use of this variable 

 factor. 



It seems, my " explanation of the effect of a uniform wind blow- 

 ing across a whirler upon which an anemometer is being tested is 

 very surprising ; " indeed, I have wondered myself that so simple 

 an explanation had not been suggested long ago. That it is " en- 

 tirely untenable " cannot be admitted, since it is only made to ap- 

 pear so by my critic, who unfortunately omits from the very heart 

 of the statement whose accuracy he questions, three very impor- 

 tant words. Nothing more than this need be said. I am well 

 aware, also, that " it has generally been considered that while these 

 cups [of the anemometer] never respond instantly to the wind, and 

 continually lag behind while the wind is rising, yet their momen- 

 tum keeps them up, and about counterbalances this lagging while 

 the wind dies down ; " but that these effects about balance is ex- 

 actly what does not occur, and therein is the novelty of the ex- 

 planation I have suggested. 



The substitute offered in Science of April 5 (p. 268) is based 

 partly on an incorrect statement ; namely, that a wind blowing 

 directly at right angles to the path along which an anemometer is 

 being carried will add its effect to that due to the motion of the 

 anemometer. If the writer means that the sum of the two separate 

 effects are to be taken, he is entirely wrong. It is a simple question of 

 the resultant of two forces at right angles to each other, which is not 

 the sum of the two separate forces. With this as a partial basis, the 

 explanation is developed, and the astonishing conclusion reached 

 that " the anemometer will be accelerated during more than three- 

 fourths of the rotation [presumably of the whirler], and retarded 

 during less than one-fourth of it." Had the author, in accordance 

 with the principle of the parallelogram of forces, found the result- 

 tant of the two wind effects that act simultaneously upon the ane- 

 mometer at each point of its path, and integrated or summed these 

 up for a complete revolution of the whirler, he would doubtless 

 have arrived at a much more accurate conclusion, — a conclusion 

 that the ultimate resultant effect for a whole revolution " is only 

 small in most cases, and is not very serious," as given in my 

 original letter in Science of March 29 ; a view, moreover, that is 

 entertained by Professors Dines, Stokes, and others who happen to 

 have written on the question. 



Even admitting that the explanation under discussion is correct, 

 it does not account for the uniformity of the results obtained in 

 England with the helicoid anemometer, which, being provided with 

 a vane or tail, always presented its front directly to the resultant 

 wind. The Robinson anemometer, from its construction, has no 

 need of a tail, and the two instruments are circumstanced exactly 

 alike so far as being equally subject to the resultant wind. It is 

 presumed throughout this and previous papers that the axis of the 

 Robinson anemometer is vertical or nearly at right angles to the 

 plane of rotation of the whirler. The analysis of the problem is a 

 little different when the axis is inclined more or less to the vertical, 

 but the final result is practically the same. 



Having several weeks ago submitted a paper containing in detail 

 the various experiments and results that led to the development of 



the explanation given in Science of March 29, I do not desire to 

 cite here any experimental confirmation of the theory, nor do I 

 consider that the results given by Professor Hazen in any way dis- 

 prove the theory. Why one should expect to be able to use the 

 same formula for cone-shaped paper cups as had been found appli- 

 cable to hemispherical metal cups, or should be surprised at a dif- 

 ference of twenty per cent less wind-velocity, does not appear. 



Following the example of Professor Hazen, I intend to try some 

 experiments with hemispherical paper cups, and have thus far 

 completed a set ; but the pressure of other duties has not afforded 

 me opportunity to do more as yet. C. F. Marvin. 



Washington, D.C., April 8. 



The Metric System and Professional Teaching. 



The committee appointed at the Cleveland meeting to consider 

 the relations of chemistry to public instruction, naturally have their 

 attention called to the metric system of measures. No doubt the 

 familiarity of the public with this system has much increased since 

 1866, when the Act of Congress was passed making it legal ; but 

 recent conversations with parties who might be supposed well 

 posted on the subject show some views that appear to the writer 

 incorrect, and adapted to retard the adoption of a much-needed re- 

 form. 



A very prominent teacher of chemistry said he was not an advo- 

 cate of its general use, and that no time would be saved in the 

 instruction of children by such adoption. The Metric Bureau, in 

 their leaflet, stated that " a year of the school-life of every child 

 would be saved by the adoption of this system." This state- 

 ment was made by teachers. I do not know its basis ; but there 

 are, in the English system of tables we -use, about fifty factors to 

 be memorized. As there is but one factor in the metric system, 

 and that the same as our system of numeration, necessarily fifty 

 times as much time is required to learn English measures as metric. 

 If the Society for Psychical Research can tell us the average time 

 required to memorize an idea, we should then know the saving of 

 time in instruction, that would follow the adoption of the metric 

 system. 



An apothecary assured me that the adoption of parts by weight 

 in the new pharmacopoeia, with which he connected in some way 

 the metric system, had, in his judgment, done great harm to the drug 

 business : for, he said, the wholesale manufacturers put on the 

 outside of their bottles that one part of this extract, etc., with nine 

 parts distilled water (or required proportions), would make ten vol- 

 umes of the officinal strength. The extreme simplicity of this 

 process, my friend argued, reduced the drug business, so far as 

 intellectual qualifications are concerned, below the grocer, and the 

 metric system was somehow held responsible. 



The metric system is in universal use by chemists. The arts of 

 medicine and pharmacy are dependent on chemistry for their ma- 

 terials and their processes. As matters now stand, every student 

 in the colleges of these arts is obliged to learn two new tables of 

 measures, — apothecary and metric ; for I assume that all profes- 

 sors of chemistry teach the metric, and some professors of materia 

 medica also. In other schools the chair of chemistry teaches one, 

 and the chair of materia medica the other system. 



Is it not time to inquire if this is a rational condition of things ? 

 It will not do to say the apothecary weight is learned in the pri- 

 mary school. The metric is taught also, at the present time. Both 

 are usually forgotten before the student matriculates. Neither can 

 it be said that we break away from the system of our English cou- 

 sins, for our fluid measures are not the same as theirs, now that 

 they use the imperial gallon. There remains the single argument 

 against the metric system in our professional schools, that it is not 

 in general use by physicians. Those who do use it find the gram 

 aVnost convenient unit. The difficulty of inducing a large body of 

 men to change some of their basic elements of thought seems to be 

 the greatest obstacle to a beneficial improvement. 



Now, why not let the old doctors use the old system, but teach 

 the graduates only the new ; then add to the pharmacy laws a 

 clause requiring every druggist to provide himself with a set of 

 metric weights, making this condition as indispensable as a di- 

 ploma ? At present, when a prescription is presented in the met- 



