PHYSICS. 585 



for some of these points and for some lying in the curve. Except in 

 one case, the departures are less than the maxinuim differences afforded 

 by the dei^ressions observed on a single tliermouieter. In this case, the 

 only one where the depression is diminished, the lime, soda, and potash 

 exist in the glass in nearly equal amounts. {Am. J. Sci., May, 1885, 

 III, XXIX, 385.) 



Bartoli has sought to show the non-permeability of glass to gases by 

 means of a polarization test. A glass trough divided vertically in the 

 middle was filled with a solution of sodium sulphate. On opposite 

 sides of this partition were fastened thin gold electrodes, a second elec- 

 trode, also, ot gold, being in each cell. The two electrodes of one of these 

 cells were connected with a delicate galvanometer, those of the other 

 with a strong battery. But no effect was produced upon the galvanom- 

 eter. Since any trace of either oxygen or hydrogen by passing through 

 the glass would have polarized one of the galvanometer electrodes and 

 produced a current, the author concludes that the glass is not permea- 

 ble to gases. {11 Nuovo Cimento, III, xvi, 78 ; J. Phys., December, 1885, 

 II, IV, 556.) 



Trowbridge and McEae have determined by several methods the co- 

 efficient of elasticity of ice. Bars prepared by freezing water in metallic 

 tubes were vibrated transversely and made to record their vibrations 

 oimultaneously with those of a tuning fork of known pitch. The values 

 of E in two experiments were 60 x 10*^ and 55 x 10^ absolute units. 

 Bars of ice were cut from a pond, sui)ported at the ends, weighted, and 

 the deflection measured by a cathetometer. The values in the four 

 series of observations were 57 x 10^ 05 x 10^, 71 x 10», 96 x 10^, 

 the mean being 72 x 10^. By the method of longitudinal vibrations, 

 the pitch of the note being 0,3 of a semi-tone of C sharp, the modulus 

 for a bar of ice 138 centimeters long was found to be 86 x 10" absolute 

 units. The calculated velocity of sound in ice is therefore 2,900 meters 

 per second, or about nine times the velocity in air. {Am. J. Sci.^ May, 

 1885, III, XXIX, 349.) 



Trotter has communicated to the Royal Society the results of some 

 experiments made at the Grindelwald glacier to ascertain whether di- 

 rect evidence of shearing could be obtained in ice under the action of 

 forces produced by the action of gravity. Bars of ice were passed 

 through holes in three parallel blocks of wood nearly in contact, the 

 two outer ones being hung to a frame, while a weight was hung to the 

 middle one. In a final experiment a shear of about 0.075"" was observed 

 after the action during seventeen days of a shearing force of rather more 

 than 200 grams per square centimeter. He therefore thiidvs that " there 

 is little doubt that, under conditions closely resembling those in the in- 

 terior of a glacier, and under the influences of forces comparable with 

 those which gravity is capable of exerting in a glacier, hand s])ecimens 

 of ice shear in the same manner as a truly viscous solid would do." 

 {Kalure, February. 1885, xxxi, .328.) 



