202 M. A. Bitter's Contributions to the Study 



I find the convenience and certainty of action far overbalance 

 this. 



I send it in the hope that you may find it useful ; but should 

 you know of any more convenient electric generator, I shall 

 be much obliged if you will let me know. On the other hand, 

 if the foregoing is something new and you think it worth pub- 

 lication, I leave it entirely in your hands to do as you like. I 

 had hoped to be able to send you a copy of some work I have 

 been doing with the spectroscope ; but the mail closes before I 

 am ready, and I await another opportunity. 

 Believe me, my dear Sir, 



Yours faithfully, 

 Dr. Iluggins, H. C. Russell. 



$*c. fyc. 



XXIX. Contributions to the Study of States of Aggregation. 

 By A. Bitter *. 



[Plate VIII. figs. 1-13.] 

 § 1. Temperature-surface of Air. 



IF a kilogram of air at rest is confined in a cylinder by a 

 movable piston, its pressure p, volume v, and absolute 

 temperature T are, by the gaseous laws, connected by the 

 the equation 



pv=HT, . '. ... . . (1) 



the constant B being equal to 29*27 when v is expressed in 

 cubic metres andjo in kilograms weight per square metre. 



This equation shows that the quotient —■ has always a con- 

 stant value, however the state of the air may be altered by 

 shifting the piston or applying heat. 



For the absolute temperature of the air we have from the 

 above equation the expression 



T=f (2) 



The magnitude T appears in this equation as a function of 

 the two variables p, v ; and the law of the alteration of T with 

 p and v can be exhibited geometrically by a curved surface. 

 If the point in the horizontal plane OXY whose coordinates 

 are p, v is found, and a perpendicular to the plane of length 

 T drawn through it, the extremity J of this perpendicular 



* From Poggendorff's Annalen, No. 10, 1877 ; translated and commu- 

 nicated by Robert E. Baynes, M.A., Senior Student of Christ Church., 

 Oxford, and Lee's Reader in Physics. ' 



