In regard to the three classes into which the variables were divided, the mean distances of the stars from the center of the cluster of the different groups are 7.7', 8.1' and 8.9'. It appears, therefore, that no marked difference is indicated in the distribution, on account of the character of the light changes. The mean maximum brightnesses of the three classes are 12.99, 13.10 and 13.33 magnitudes, and the minimum, 14.11, 13.97 and 13.89 magnitudes. The amplitudes are thus distinctly different. The mean lengths of the periods are 0.58617, 0.75153 and 0.39463.

It is of great value that for the 95 variables whose periods are determined the light curves are given not only graphically in Plates II. to VII., but that the coordinates of the lightcurves are given in detail on pages 210 to 222, and in such a way that for each star the period is divided into 24 equal parts, and for each part the corresponding brightness is given. There are also given typical light tables for the three classes, by taking from each class five especially characteristic examples, and taking the mean values for these.

The chapter closes with some remarks concerning the possible causes of the light changes of so many stars in one and the same cluster. The author hesitates to accept widely current hypotheses, and to test them from the available materials of observation. He concludes only that from the complete uniformity of the periods, which is shown in w Centauri for a long time, the variability must be associated with some regularly returning phenomenon, either through regular eclipses by bodies which are in revolution about each other in definite paths, or through the rotation of unequally illuminated or irregularly shaped bodies. The explanation by means of occultations, as with Algol stars, involves great difficulties. For, if one would assume, as at first sight might appear plausible, that the planes of the orbits of the different double star systems of the cluster lie about parallel to each other, and that on that account the light-curves of the different systems should show a certain similarity, the form of the light-curves, nevertheless, speaks against the eclipse theory. In a Centauri are found three different types of light-curves, but in other clusters investigated by the author the first type with the long duration of minimum is so much more common that we may regard this as the characteristic type of variables in star clusters. This type of light-curve is, however, entirely distinct from the Algol type. The eclipse would have to last for a considerable part of the period, and this would hardly be consistent with any orbit system. Also the assumption of an axial rotation with unequally luminous surfaces seems not very probable, when one considers that such a large number of similar variables is concerned. The whole phenomenon is at this time somewhat enigmatical, and we must await the investigation of the occurrences in other clusters before further conclusions are permissible.

In an appendix to the volume are given preparatory studies toward the measurements of all those clusters in which more than one variable has been found. There are given the positions of those objects selected to serve as fundamental stars, and the comparison stars

chosen for the comparisons of brightness, and the stars already known to be variable, all the positions being given in seconds of arc, and determined from the center of the particular cluster. In Plates VIII. to XII. are given reproductions from the original plates of fourteen clusters, on which the variables and comparison stars are marked. On these reproductions 1 mm. equals about 10". Especially interesting are the repeated enlargements of certain portions of some clusters, which are given in the last plate of the volume. These show clearly the change in appearance of the variables on different plates, and give an idea of the certainty with which the comparison with adjacent stars can be made.

From the materials given in the appendix one sees that there still remains a very great amount of labor to be done. We hope that the author will be able to carry out his plan, and to give as clear and exhaustive a discussion of the light changes in the other star clusters, as he has done in the present volume.* G. MÜLLER.

SCIENTIFIC JOURNALS AND ARTICLES. THE contents of the American Journal of Science for November are as follows: 'Mineralogical Notes,' by C. H. Warren; 'Studies of Eocene Mammalia in the Marsh Collection, Peabody Museum' (with plates XVI. and XVII.), by J. L. Wortman; Tridenum Virginicum (L.) Rafin,' a morphological and anatomical study (with figures in the text), by T. Holm; Ephemeral Lakes in Arid Regions,' by C. R. Keyes; 'Note on the Identity of Palacheite and Botryogen,' by A. S. Eakle: 'Colloidal Gold: Absorption Phenomena and Allotropy,' by J. C. Blake.

After a few remarks by the chairman, Professor Miller, outlining the policy of the section for the ensuing year, and requesting members to present papers in abstract as far as possible, so as to have more time for discussion, the following papers were read:

The Volumetric Determination of Zinc: W. J. WARING.

This paper was read by Mr. Stone and discussed by Messrs. Brenneman, Stone, Miller and Danziger. It called attention to the widely differing results which are obtained by different chemists in the determination of zinc by the ferrocyanide titration method, and pointed out the necessity of uniformity in the conditions of standardizing and titrating, so that the composition of the precipitate shall be uniform.

The occurrence of cadmium in the ores of the Joplin District in amounts varying from 0.1 to 2 per cent. was shown to interfere with the accuracy of the method, so that the cadmium should be removed, best by aluminum foil, before the titration. A new cadmium ammonium ferrocyanide was also described. The Reduction of Lead from Litharge in Preliminary Assays and the Advantages of an Oxide Slag: E. H. MILLER, E. J. HALL and M. J. FALK.

Professor Miller gave an abstract of an article which will soon appear in the Transactions of the American Institute of Mining Engineers. It was shown in making preliminary assays to determine the reducing power of an ore that, not only did the amount of lead reduced vary with the acid or basic character of the slag, but that the amount of lead oxidized by niter varied with the reducing agent present, even under uniform conditions as to charge, time and temperature. This was not anticipated, and explains the difficulty in the old preliminary assays.

The best results were obtained by using a charge of ore 3 grams, litharge 50 grams, soda 10 grams, no silica, no borax glass and no salt cover. With this charge and a temperature of over 900° C. the sulphur is completely oxidized to sulphate and forms an upper layer in the slag (Na,CO, and Na,SO,), while the lower layer consists of a readily fusible misture of oxide of lead, of iron, etc.

This style of charge was then tested with a quantity of ores containing sulphur combined with iron, copper, zinc and lead. The charge for the final assay was ore 1/2 assay ton, litharge 70 grams, soda 15 grams. Niter as calculated for a 20-gram button (from the results of the preliminary assay). The buttons were soft, malleable and weighed from 17-23 grams, while the results in gold and silver were slightly higher than the old methods and the loss in the slag slightly less.

The Influence of Diet, Muscular Exertion and Loss of Sleep upon the Formation of Uric Acid: H. C. SHERMAN.

Observations made in connection with metabolism experiments upon three professional athletes and one subject of sedentary habits showed the quantity of uric acid eliminated to be primarily dependent upon the quantity of meat products in the diet, and to be influenced very little, if any, by the abundance of a bread and milk diet, by a considerable loss of sleep, or (in the case of the professional athletes) by long-continued muscular exertion. With the subject of sedentary habits, a much smaller amount of exercise increased slightly the uric acid elimination. This paper will appear in the November issue of the Journal of the American Chemical Society.

H. C. SHERMAN, Secretary.

ELISHA MITCHELL SCIENTIFIC SOCIETY.

Ar the 150th meeting of the Elisha Mitchell Scientific Society, held in the Chemical Lecture Room of Person Hall, University of North Carolina, October 13, the following papers were presented:

The Use of the Vector Diagram in Electrical Engineering: Mr. J. E. LATTA.

Tanning (with specimens): Professor CHARLES BASKERVILLE.

After outlining modern methods of tanning, especially by the use of chromium nitrite, a number of rare skins which had been done for Messrs. Tiffany & Co., of New York, were exhibited. The skins were presented to the Museum of the Chemical Laboratory.

The Influence of the Spermatozoon on the Larval Development of the Sea-Urchin : Professor H. V. WILSON.

A New Indicator: Professors E. V. HOWELL and A. S. WHEELER.

A new indicator extracted from the hulls of the muscadine or wild Bullace grape was announced. This coloring matter gives a red color with acids and green with alkalies, being purple in neutral solutions. The only solvents so far found which may be used for its extraction are alcohol and water. It responds to inorganic and organic acids and volatile and non-volatile alkalies. Carbon dioxide does not affect it.

On adjournment of the public session, the annual meeting was held for the election of officers and transaction of business. The pro

posed agreement with the North Carolina Academy of Science was approved. By this agreement the Journal of the Mitchell Society becomes the official organ of the North Carolina Academy of Science, its size being doubled and issued quarterly. The following officers were elected for the ensuing year:

President-Professor Charles Baskerville.
Vice-President-Mr. J. E. Latta.

Recording Secretary-Professor A. S. Wheeler. President Venable retains the permanent secretaryship. CHARLES BASKERVILLE, Secretary.

DISCUSSION AND CORRESPONDENCE.

A HITHERTO UNDESCRIBED VISUAL PHENOMENON.

TO THE EDITOR OF SCIENCE: The phenomenon of apparent movement described by Dr. Gould (SCIENCE, XVIII., 536) was discussed in 1896 by Professor S. Exner in an article entitled 'Ueber autokinetische Empfindungen' (Zeits. f. Psych. u. Physiol. d. Sinnesorgane, XII., 313). According to Exner, the first observation on record was made by Alexander von Humboldt in 1799. Several authors (among them men as well known as Aubert and Charpentier) have occupied themselves with the phenomenon; and it forms the subject of an experiment in Sanford's Laboratory Course, 1898, 309.

E. B. TITCHENER.

SHORTER ARTICLES.

PHOTOTROPISM UNDER LIGHT-RAYS OF DIFFERENT

WAVE-LENGTHS.

THE effect of lateral incidence of light upon Cormophytes is of such a nature as to produce a tendency in the plant to arrange its axis parallel to the direction of the incident ray. This response to the stimulus of light is quite general with regard to higher plants, and has long been known under the name heliotropism. The term phototropism-from its literal meaning more appropriate has recently been introduced to displace the older term.

*

The relative phototropic effects of rays of different wave-length have been given by Wiesner to be greatest between ultraviolet and violet rays, diminishing gradually over to the yellow, where it disappears, then beginning in the orange and reaching a small secondary maximum in the ultra-red. Guilleman'st results resembled those of Wiesner excepting with respect to the yellow. He concluded that curvature takes place under all the rays except the least refrangible heat rays. Sachs himself states that under blue light curvature takes place as in ordinary daylight, and that no curvature whatever takes place behind a ruby-red glass; and he agrees with Wiesner that no curvature takes place behind a yellow screen.

With regard to the decoloring effect upon a fresh alcoholic solution of chlorophyll by rays of different wave-length, the present position is practically that expressed by Vines :+ 'Sachs and Wiesner have ascertained that the rays of low refrangibility are more active in forwarding it than those of high refrangibility.'

Some investigation of these subjects has been made by the writer, and the results are here given because they differ materially from those referred to, and because it is thought the methods here used to test the matter are less open to objection and more complete than those of the authors mentioned above.

The following named glass plates (each nine *Die Heliotrop. Erschein. im Pflanzenreich.' † Ann. de Sci. Nat., IV.; 7; 1858. Both referred to by Sachs, Plant Physiol.,' p. 696.

'Lectures on Plant Physiol.,' p. 266.

by twelve inches) were secured from Bausch and Lomb and are what are commonly called standard colors '-violet, blue, green, yellow, red-several of each. Window-glass was used to admit daylight, and sheet iron for the opaque screen. These colored plates were examined by the writer with a view to getting the particular spectrum of each, because colored glass can scarcely be represented accurately by simply naming the 'color'; for certain colored screens allow other colors' to pass than that which would seem from ordinary observation. The curve for each 'color' is plotted approximately in the accompanying

effects of the screens mentioned, a number of metal frames were made so as to admit of free insertion of any of the plates into any of the four vertical sides of the frame. The plant to be used in the test was placed within the frame and enclosed on two opposite sides by opaque screens, and on the other two vertical sides were placed plates of two different 'colors.' On the top and the bottom were opaque plates. Then the plant was enclosed within the lantern' and placed equally distant from the two color-screens. No light was admitted to the plant excepting that coming through the two screens; and, since the top was covered, the plant was subjected to lateral illumination from two different 'colors' at the same time and from opposite directions. Care was taken to have only diffused daylight enter the screens and to have it equal in intensity. Now it seemed reasonable to conclude that if curvature of the stem of the plant took place toward one of the colored screens, the light which penetrated that screen produced most phototropic stimulus. The lanterns, not being actually air-tight, permitted the plant to live under more natural conditions of temperature, moisture and air than could be obtained by means of a double bell-jar.

The results obtained are summarized as follows and are represented by the curve given in Fig. 2, I. They rank in order named: blue, white (window glass), violet, green, yellow, red, dark (opaque). Between certain pairs of these screens the difference is not very great, but there is a positive difference in every case. The main differences between these results and those of Wiesner, Guilleman and Sachs are in regard to the blue, the yellow and the red. Sachs states, p. 696, that curvature takes place behind a blue solution of ammoniacal oxide of copper as in full daylight. This is scarcely exact, because curvature is more prominent behind the blue screen than behind diffused daylight. It is also shown clearly here that curvature does take place behind red and behind yellow, though they produce less of a phototropic stimulus than any of the others, the yellow being stronger than the red. Wiesner states that no curva

fresh alcoholic solutions and in each test the solutions were of exactly the same concentration, but solutions of different degrees of concentration were used to see if strength of solution had anything to do with the results. The conclusions reached were as summarized in Fig. 2, I, and in the following order commencing with the quality of light having the greatest decoloring effect: 1, Diffused light (in no case was direct sunlight used in the test); 2, yellow; 3, blue; 4, red; 5, violet; 6, green; 7, darkness. The result of this experiment showed that there was but small relationship between the phototropic effects and the decoloring effects upon chlorophyll in solution. It is quite clear that there is little in common (see Fig. 2, I and II). Sachs and Wiesner both say that the rays of low re