PHYSICS. (S07 



author to represent best the results is of the form l\—l-\-at-\-iit''+yt^, in 

 which ia= — 0-000731275C, y= + 0-0000079327, and ^r= — 0-00000002C79, 

 At being the true specific heat at U. This indicates that the specific heat of 

 water has a minimum value at 43.5^ and a maximum at 104.5°. ( Wicd. 

 Ann., XXI, 31 ; J. Fhys., November, 1885, II, iv, 521.) 



Berthelot and Vieille, in their studies on the heat relations of the ex- 

 plosion of gaseous mixtures, have been able from the data obtained 

 to calculate the specific heat of the elementary gases, of water and of 

 carbon dioxide at high temperatures. Thus, for the simple gases Njj, 

 H2, and O2, as well as the compound gas CO, which is closely related to 

 them, the specific heat at 2,8()0o is 0-7 ; at 3,200°, 7-9; at 4,000°, 8-4; 

 and at 4,400°, 9-3. It will be observed that it increases rapidly with tlie 

 temperature, being doubled, nearly, between 0° and 4,500°. The mean 

 specific heat of water between 0° and 2,180° is 1557, and between 0° and 

 3,240°, 18-12. Hence the mean specific heat between 130° and 230° is 

 more than doubled at 2,000° and tripled at 4,000°. For carbon dioxide 

 the mean value between 0° and 2,900° is 20-5, and for cyanogen, between 

 0° and 4,300°, 22*5. The specific heat of the former gas more than 

 triples and the elementary specific heat quadruples between 0° and 

 4,:i00°. (Ann. Chim. P/^i/s., January, 1885, VI, iv, 66, 74; Am, J. ScL, 

 April, 1885, III, xxix, 331.) 



Bar toll has described a simple form of apparatus for lecture demon- 

 stration to show the equivalence of heat and work. Two small globes, 

 one containing mercury, the other benzene, are connected by a narrow 

 tube, from which rises perpendicularly a thermometer tube, graduated. 

 On placing the mercury globe vertically above the other, the mercury 

 flows through the tube into the lower globe, the energy of its fall being 

 converted into heat, which exi)ands the benzene by an amount easily 

 read off on the fine tube. The calibration of this tube may be effected 

 by passing a known current through a wire of known resistance sealed 

 in one of the balloons, and calculating the heat evolved. (11 Nuovo Ci- 

 mento, XV, 18; J. Pliys., December, 1885, II, iv, 558.) 



Webster has experimented to determine the mechanical equivalent 

 of heat by observing the thermal effect produced by the electric cur- 

 rent on a thin ribbon of steel, the temperature being measured from the 

 change in resistance. The final value obtained was 4-14 x 10" ergs per 

 gram-degree. {Proc. Am. Acad., May, 1885; Fhil. Mag., August, 1885, 

 V, XX, 217.) 



LIGHT. 



1. Production and Velocity. 



The following is the conclusion leached by De Volson Wood after an 

 extended discussion of the properties of the luminiferous aether as de- 

 duced from the best obtainable data : " We conclude then that a medium 

 whose density is such that a volume of it equal to about twenty volumes 

 <»f the earth would weigh 1 pound, and whose tension is such that the 



