Ix GENERAL SUMMARY OF SCIENTIFIC AND 



perimental results given accord well with those calculated on this 

 theory. 



Terquem and Trannin have described a new method for deter- 

 mining rapidly the index of refraction of a liquid, which, like Wol- 

 laston's, depends upon the angle of total reflection, but which does 

 not require a special apparatus. By means of two plane parallel 

 plates of glass, having a film of air between them, which are im- 

 mersed in the liquid to be examined, the critical angle is deter- 

 mined, and so the index. 



Hagenbach has called attention to the fact that unannealed or im- 

 perfectly annealed glass, which is in a state of tension from too rapid 

 cooling, is very likely to break either from a blow or from sudden 

 changes of temperature. As this tension renders the glass doubly 

 refracting, he proposes to examine glass articles with polarized light 

 in order to detect any imperfection in the annealing. 



Gaumet has devised a new telemeter, or distance measurer, which 

 is small enough to be carried in the pocket, and which gives the dis- 

 tances it measures to within one fiftieth of their actual value. Even 

 this may be exceeded by using an observing telescope. It is founded 

 on doubly reflecting the object from two mirrors placed at 45 from 

 each other, one of which is movable. By means of a base-line, and 

 the angle formed by the lines drawn from the distant object to the 

 extremities of the base-line, the distance may be calculated. 



Salet has investigated anew the question of spectra of different 

 orders. He combats the view of Schuster that nitrogen ceases to 

 give the characteristic channeled spectrum after being heated with 

 sodium, and shows, first, that the spectrum in question can be ob- 

 tained from nitrogen heated in contact with sodium ; second, that 

 the disappearance of this spectrum in the experiment is due to the 

 disappearance of the nitrogen itself, it being absorbed by the sodium 

 under the influence of the electric discharge ; and, third, that the 

 spectrum described by Schuster is really due to vapors of the alkali- 

 metal. 



Potier has examined mathematically the question of the influence 

 which the motion of matter exerts upon luminous ether waves. 



Salet has examined the spectrum of nitrogen and of the alkali 

 metals in Geissler tubes. He observed that sodium sealed with ni- 

 trogen in a tube under a slight pressure did not always cause the 

 disappearance of the bands in the nitrogen spectrum, but that it 

 appeared even to absorb the nitrogen and to become black. This 

 nitride, treated with water, gave the reactions of ammonia. In his 

 opinion, therefore, the bands in the nitrogen spectrum are not changed 

 when treated with sodium, unless the nitrogen is actually absorbed 

 by the sodium, when the spectrum changes, of course, to that of so- 

 dium vapor, which was the spectrum supposed by Schuster to be that 

 of nitrogen. 



