150 ANNUAL OF SCIENTIFIC DISCOVERY. 



10 atmospheres, the second is perfectly empty. When a communica- 

 tion is suddenly made between the two reservoirs the gas expands to 

 double its volume, and the pressure is reduced to 5 atmospheres. In 

 these two experiments then, the initial and final conditions of the gas 

 are the same : but this identity of condition is accompanied by calorific 

 results which are very different for while in the former experiment 

 there is a reduction of temperature, in the second the calorimeter does 

 not indicate the slightest alteration of temperature. 



M. llegnault then gives a table of specific heats of various elastic 

 fluids, the result of his own experiments. Some of these are widely 

 different from the result hitherto obtained by other experimenters. 

 The following are the more important : 



' Specific New Former Specific New Former 



beat of: Experiments. Exp'ta. heat of : Experiments. Exp'ta. 



Water 1,000 .... 1,000 



Atmospheric Air. . . . 237 267 



Oxygen 218 236 



Nitrogen 244 275 



Hydrogen 3,405 3,294 



Carbonic Acid 216 221 



Carbonic Oxyd 248 288 



Water Vapor 475 847 



Alcohol Vapor 451 



Ether Vapor 481 



Chloroform Vapor .. 157 



The specific heat of air has been found the same at different temper- 

 atures, from 30 deg. below zero to about 500 deg. above it, and under 

 pressures varying from one to ten atmospheres. The specific heat of 

 steam is given at about one half the number formerly assigned to it. 



ON THE OSCILLATORY THEORY OF LIGHT. 



IN a paper on the above subject read before the British Association, 

 by Mr. J. Rankine, the author endeavors, while retaining the whole 

 of the mathematical forms of the undulatory theory of light, to render 

 the physical hypothesis which serves as its basis more consistent with 

 itself and with the known properties of matter. Light, according to 

 the undulatory theory in its most general sense, consists in the pro- 

 pagation of some species of motion amongst the particles of the 

 luminiferous medium, the nature and magnitude of which motion are 

 functions of the direction and length of certain lines transverse to the 

 direction of propagation. According to the existing hypothesis of 

 vibrations, this motion is a vibration of the atoms of the luminiferous 

 medium in a plane transverse to the direction of propagation. In 

 order to transmit motions of this kind, the parts of the luminiferous 

 medium must resist compression and distortion like those of an elastic 

 solid body ; its transverse elasticity being great enough to transmit 

 one of the most powerful kinds of physical energy with a speed in 

 comparison with which that of the swiftest planets of our system is 

 appreciable, but no more, and its longitudinal elasticity immensely 

 greater, - - both these elasticities being at the same time so weak as to 

 offer no perceptible resistance to the motion of the planets and other 

 visible bodies. The author considers that it is impossible to admit 

 this hypothesis as a physical reality. He also points out the difficulties 



