712 



SCIENCE. 



[N. S. Vol. XV. No. 383. 



Pylaie first described them. Interesting speci- 

 mens of Agarum^ Alaria, Porphyra, Gloiosi- 

 phonia, etc., were exhibited, the Agarum from 

 a deep tide-pool at Digby covered by thirty feet 

 of water at high tide. Corallines attain great 

 beauty in these northern waters, and with the 

 attendant brown rockweeds and lustrous kelps 

 lend great richness and diversity of color. The 

 dulse gatherers were found to distinguish and 

 prefer the dulse growing on Laminaria to that 

 attached to rocks. Dulse gathering at Pictou 

 forms a business of considerable importance; 

 the dried dulse is put iip in barrels to be sold 

 in Boston and latterly in New York. 



A third communication, by Dr. MacDougal, 

 consisted of the exhibition and discussion of a 

 specimen of Ephedra, one of two species col- 

 lected by him in his recent trip to Arizona. 

 This remarkable leafless relative of the pines 

 produces palisade cells along its stems instead 

 of leaves. A living cutting about three feet 

 high was shown resembling Scotch broom in its 

 multitudes of long green and brown branches. 



Dr. MacDougal also exhibited a remarkable 

 Arizona plant, perhaps an Ipomma, with large 

 swollen discoid base about fifteen inches in 

 diameter, to which short roots were still 

 attached. He had also collected there the tree 

 Ipomcea known as the 'Palo Blanco' tree, on 

 which deer browse; it bears a few flowers all 

 the year round, but the leaves disappear after 

 the rainy season. Edward S. Burgess, 



Secretary. 



UNIVERSITY OF WISCONSIN SCIENCE CLUB. 



At the meeting of the Club held on 

 April 1, Professor E. W. Wood, of Johns 

 Hopkins University, addressed the Club on the 

 subject 'A Suspected Case of the Electrical 

 Pesonance of Minute Metal Particles for Light 

 Waves, — A New Type of Absorption.' 



Small pieces of sodium, lithium or potas- 

 sium heated in air-exhausted glass bulbs 

 deposit on the cold wall of the bulb in the 

 form of a film which shows colors by trans- 

 mitted light as strong as those produced 

 by the aniline dyes. The color does not 

 seem to depend on the thickness, and all 

 attempts to explain it by the well-known 

 principles of interference have been without 



success. The microscope shows that the de- 

 posit is made up of exceedingly minute grains, 

 which are but just barely visible under 

 a one twelfth inch oil immersion objective. 

 Their diameter is not far from .0002 mm. The 

 colors vanish on the admission of the smallest 

 trace of air. They change in a most remark- 

 able manner if the outside of the bulb be 

 touched with a small piece of ice, or if the 

 glass be locally heated. The change of color 

 produced by the application of ice to the out- 

 side of the bulb is always in the direction 

 corresponding to a drift of the absorption band 

 towards the red end of the spectrum. A purple 

 film which has an absorption band in the yellow 

 becomes blue-green when cooled, the absorption 

 band moving into the red. 



The cause has been found to be a condensa- 

 tion of the traces of volatile hydrocarbons 

 (derived from the metal) on the colored film, 

 thus immersing the particles in a fluid of high 

 dielectric constant, the efFect of which would 

 be to increase the capacity of the system, lower 

 the period of vibration, and move the region 

 of absorption towards the red end of the spec- 

 trum. This was proved by forming the film 

 in one half of a double bulb and immersing the 

 other half in solid CO, and ether, thus bring- 

 ing down all the hydrocarbon vapor. The 

 colored film was found to be no longer sensitive 

 to the local application of ice. It became 

 sensitive, however, as soon as the lower bulb 

 was removed from the freezing mixture and 

 warmed. Sometimes the film becomes nearly 

 colorless when cooled, the absorption band 

 moving out of the visible spectrum entirely. 

 Films originally pale apple green become deep 

 violet when cooled, the color being as deep as 

 that of dense cobalt glass. Various experi- 

 ments have been tried with polarized light at 

 different angles of incidence. 



The paper will appear in full in the Proceed- 

 ings of the London Physical Society and the 

 Philosophical Magazine. C. K. Leith. 



DISCUSSION AND OORBESPONDENOE. 



THE MATHEMATICAL THEORY OF THE TOP. 



To THE Editor of Science: 'The Mathe- 

 matical Theory of the Top,' kindly communi- 

 cated for me by Professor Barus to Science of 



