June 22, 1900.] 



SCIENCE. 



995 



atmospheres, etc. These pairs of temperatures 

 and pressures represented by ordinates and ab" 

 scissas determine a curve. This curve is called 

 the transition curve (umwandlungs curve) for 

 water and ice. Herr Tammann has followed 

 the transition curve for water and ordinary ice 

 far beyond the region previously knOwn, in 

 fact throughout its entire extent, and he has 

 determined portions of the transition curves of 

 water and ice II., of water and ice III., of ice I. 

 and ice II., and of ice I. and ice III. He has 

 also determined the latent heats of fusion of ice 

 II. and of ice III., the latent heats of transition 

 from ice I. to ice II. and from ice I. to ic6 III,, 

 and the changes of volume during these various 

 transitions. 



Readers of Science who are not familiar 

 with recent work in physical chemistry may be 

 interested to know that many solid substances 

 are known which have two or more forms 

 (phases). Thus, very recently, it has been 

 found that metallic tin may exist as a gray 

 crystalline powder or in the well known form 

 having lustre and ductility. At a certain tem- 

 perature (under atmospheric pressure) these 

 two phases may coexist in equilibrium, at 

 higher temperatures the ductile variety only 

 is stable, and at lower temperatures the gray 

 crystalline form only is stable. 



SOME EXPERIMENTS WITH POLARIZED LIGHT. 



The Annalen der Physih for May, 1900, con- 

 tains a description by N. Vmow of several 

 beautiful and instructive experiments with 

 polarized light. 



A polished cone of glass stands upon a flat 

 white screen. A beam of ordinary light paral- 

 lel to the axis of the cone is reflected by the 

 curved surface of the cone forming a circle 

 of light around the base of the cone upon the 

 white screen. If the beam of light is plane 

 polarized the circle of light will have a broad 

 dark streak across it. If a quartz plate is placed 

 in the path of the plane polarized beam the 

 planes of polarization of the various wave- 

 lengths will be diflferently turned and the circle 

 of light around the base of the cone will con- 

 sist of radial bands of color in the order red, 

 orange, yellow, green, blue, violet, purple. 



A plane polarized beam of light is reflected 

 down through milky water (obtained by mixing 

 a small portion of an alcoholic solution of rosin 

 with the water) contained in a glass cylinder. 

 To a person walking around the cylinder the 

 water would appear bright then dark then 

 bright then dark again. The two opposite di- 

 rections from which the milky water appears 

 bright mark the plane of polarization of the 

 beam of light. If now a quartz plate is inter- 

 posed in the path of the polarized beam the 

 planes of polarization of the various wave- 

 lengths will be diiferently turned and the 

 milky water will appear to be streaked with 

 vertical bands of color. A milky solution of 

 sugar substituted for the water (quartz plate 

 removed) shows a series of helical bands of 

 color. 



ON THE SIZE AT WHICH HEAT MOVEMENTS ARE 

 MANIFESTED IN MATTER. 



In his characteristically suggestive way Pro- 

 fessor G. F. Fitzgerald, in Nature, April 26th, 

 raises the question as to the maximum dimen- 

 sions of a space in which the heat movements 

 of a portion of a body in thermal equilibrium 

 might deviate sensibly from the steady average 

 which these movements show on a large scale. 

 The heat movements of matter do not show 

 their erratic character in a space large enough' 

 to be resolved by the microscope, but Professor 

 Fitzgerald points out that the accompanying 

 ether motions are much more coarse grained 

 and may give rise to sensible phenomena ; thus 

 the so-called Brownian motions of small par- 

 ticles immersed in a liquid may be caused by 

 the erratic character of heat motions in small 

 regions. He suggests further that these erratic 

 heat motions may have something to do with 

 the vitality of diatoms. Indeed it is physically 

 possible that a living cell may not be subjected 

 to the second law of thermodynamics. If so 

 in what way would a diatom be expected to 

 show its freedom from this law ? Very likely 

 in not being dependent upon food for the main- 

 tenance of its vitality, and the biologist may 

 sometime show us an organism which can live 

 in the dark without food. 



W. S. F. 



