THEKMOTICS. 607 



a power of the temperature can represent the experiments. He also 

 finds that the rule of Dalton (that as the temperatures increase in 

 arithmetical progression, the elastic force increases in geometric pro- 

 gression) deviates from the observations, especially at high temperatures. 

 Dalton's rule would be expressed by saying that the variable part of 

 the elastic force is as a', where t is the temperature. This failing, M. 

 Regnault makes trial of a formula suggested by M. Biot, consisting of 

 a sum of two terms, one of which is as a\ and the other as V : and in 

 this way satisfies the experiments very closely. But this can only be 

 considered as a formula of interpolation, and has no theoretical basis. 

 M. Roche had proposed a formula in which the force is as a z , z depend- 

 ing upon the temperature by an equation 3 to which he had been led 

 by theoretical considerations. This agrees better with observation than 

 any other formula which includes only the same number of coeffi- 

 cients. 



Among the experimental thermotical laws referred to by M. Reg 

 nault are, the Law of Watt, 4 that " the quantity of heat which is requir- 

 ed to convert a pint of water at a temperature of zero into steam, is the 

 same whatever be the pressure." Also, the Law of Southern, that "the 

 latent heat of vaporization, that is the heat absorbed in the passage 

 from the liquid to the gaseous consistence, is constant for all purposes : 

 and that we obtain the total heat in adding to the constant latent heat 

 the number which represents the latent heat of steam." Southern 

 found the latent heat of the steam of water to be represented by about 

 950 degrees of Fahrenheit. 5 



Sect. 5. Temperature of the Atmosphere. 



I MAY notice, as important additions to our knowledge on this subject, 

 the results of four balloon ascents made in 1852, 6 by the Committee of 

 the Meteorological Observatory established atKew by the British Associa- 

 tion for the Advancement of Science. In these ascents the observers 

 mounted to more than 13,000, 18,000, and 19,000 feet, and in the last to 

 22,370 ; by which ascent the temperature fell from 49 degrees to 

 nearly 10 degrees below zero; and the dew-point fell from 37 to 12. 

 Perhaps the most marked result of these observations is the following : 



s The equation z - -^ - 

 1*+ mt 



4 See Robison's Mechanical Philosophy, vol. ii. p. 8. 

 Ib. p. 160. 6 Phil. Trans. 1853. 



