WALLACE Photomicrographic and Spectrographic COLOR FILTERS The color filters illustrated here were devised by Dr. R. James Wallace, formerly PhotoPhysicist of the Yerkes Observatory and later Director of the Research Laboratory of the Cramer Dry Plate Company, primarily to enable workers in photomicrography to obtain an accurate photographic reproduction of objects, the details of which are rendered conspicuous to the eye by inherent or artificial color differentiation. By their use, the field of application of photography to bacteriology, histology, metallography and spectrography is greatly extended and the accuracy of conclusions drawn from a careful study of visual impressions, rendered permanent on the photographic plate, is increased beyond measure. The Wallace Color Filters consist of a set of ten gelatine coated glass plates two inches square, each bound with a protecting cover glass. The transmission values of these filters are the result of years of research work on the part of one who combines in a unique manner the viewpoints of both physicist and photographer, and the ranges are therefore selected to cover practically every possible combination of photographic plate and desirable or undesirable color value in the specimen to be photographed. WALLACE COLOR FILTERS, set of ten, as described above, in neat wooden case covered . $12.00 $24.00 Bulletin No. 95S, now in preparation, gives a complete explanation of the application of color filters to photomicrography and contains much information of value to those who are engaged in such work. It will be sent free upon request. CENTRAL SCIENTIFIC COMPANY 460 EAST OHIO STREET CHICAGO, U. S. A. Repeated object lessons have demonstrated that nearly all progress in science has resulted in important advances in industry G-E Research Laboratory Among the many products developed by the General For further information address Supply Department, Schenectady Office. General Electric General Office Company Sales Offices in Other Devised by Guilford L. Spencer, General Superintendent of Manufacture and Chief Chemist of the Cuban American Sugar Company, to meet the need of very rapid moisture tests in controlling the centrifugal purging of sugars and the bagasse residue in grinding sugar cane. materials are quickly dried with a minimum decomposition error, making this oven useful in factory control and general laboratory testing for moisture in materials through which a current of air can be passed. See G. L. Spencer, Journal of Industrial and Engineering Chemistry, January, 1921.¡ The oven is an arrangement for passing a large volume of air over a heating element and thence through a capsule containing the sample. The air and vapors, resulting from the evaporation, are rapidly withdrawn from the oven by a pump. The air current is induced by a small steam ejector, or powerful filter pump, or, in sugar factories, by connection with the vacuum system. It is very essential that the volume of air be large. The usual capsule is of aluminum and is ground to make a joint with the seat in the oven. The bottom of the capsule is closed with monel metal filter cloth. This cloth passes air very freely, but when it is held to a strong light the openings in it can scarcely be detected. Manifestly, capsules resistant to corrosion, and other straining material such as asbestos wool and glass wool, may be used. The temperature control is effected by means of a sliding contact rheostat, and a rheostat must always be used with the oven. This type of rheostat gives a very close temperature regulation. The heating period is so short, and the temperature variation is so small during this period, that, so far, in the sugar industry it has not been found neces sary to use a thermostat, although a tubulation is provided for one. Copy of Supplement 69, "Spencer Electric Oven," sent on request ARTHUR H. THOMAS COMPANY WHOLESALE, RETAIL AND EXPORT MERCHANTS WEST WASHINGTON SQUARE PHILADELPHIA, U. S. A. A DECADE OF AMERICAN MATHEMATICS THE year just closing carries with it into the past another calendar decade, and the fact suggests that I take up with an audience representing the mathematical section of the American Association for the Advancement of Science and the two other mathematical societies meeting with it, a sketch of the progress of our science in this country during the decade. In doing this, I am led to reflect, when I think of the struggle that has marked the period, that though it is difficult to see how a thoughtful and disinterested person can enthuse over international rivalries in territory, dominion, trade advantages or other details of national prestige which are pregnant with dangers of destruction far beyond any possible advantages gained, a desire for national preeminence in scientific attainment is most wholesome and valuable. I wish I might, therefore, compare the work of America during the decade with that of other countries. But even if this were fair, in view of the handicap the war has imposed on other countries, it would inevitably entail a sitting in judgment on questions of value over a field so broad, with so large a body of workers, that I have hesitated to assume the competency or to appropriate the time requisite to a proper performance of the task. Instead, I am restricting myself to a review of some aspects of the work of this country alone, seeking to find the directions it has taken, to find some of the respects in which it has been weak, and in which strong, and to draw a few conclusions as to strengthening it in the future. As to an anlysis of the contributions made, you will agree that since over 1,200 articles 1 Address delivered as retiring vice-president of Section A of the American Association for the Advancement of Science, at Chicago, Dec. 29, 1920. have been published since 1910, a detailed examination of those articles would be impossible. I have, as a matter of fact, obtained what I believe to be a fairly complete list of these artcles, and made a rough classification of them according to subject matter. Perhaps a quantitative comparison, based on numbers of pages, would have been more informative than one based merely on numbers of titles, but this too would have been open to criticism, and somewhat more difficult to obtain and digest. If you will bear in mind the meaning of the figures given, I have little fear that you will over-estimate their significance, or infer that I have any disposition to propose any quantitative test as the sole measure of the excellence of an individual's scientific output. On the contrary, I should prefer six pages of Fredholm's in the Proceedings of the Royal Academy of Science of Sweden of 1900 to scores of titles and many hundred pages that might be picked out from journals on the other side, or this side, of the water. The limitations on the statistical field before us must first be stated. It includes no historical, biographical, or philosophical contributions, and only such in applied mathematics as were contributed by men primarily mathematicians, or appeared in journals devoted entirely to mathematics. It does not, moreover, contain articles contributed to journals of primarily didactic emphasis. Otherwise, it is intended to be complete, and contains contributions to a considerable number of foreign periodicals. I wish to consider first the distribution of effort amongst various sub-fields of mathematics, and then to comment on some other aspects of interest presented by the data collected. In the matter of classification, in addition to certain customary headings, I have endeavored to separate out a few other classes of subjects of interest for the purposes in hand: first, certain topics whose present vitality and interest among mathematicians generally have been pointed out by Bliss, Van Vleck and others on occasions similar to this, and secondly some topics characteristically American in that Americans have taken a significant or preponderant part in their develop |