434 Mr. Herapath on True Temperature, and the [Dec. 



Article VIII. 



Tables of Temperature, and a Mathematical Development of the 

 Causes and Laws of the Phenomena which have been adduced 

 in Support of the Hypotheses of " Calorific Capacity, Latent 

 Heat" 8)C. By John Herapath , Esq. 



\(Cont'mucd from p. 388.) 



Theory of Evaporation. 

 Prop. XV. Theor.XIII. 



If T represent the true temperature of water inclosed in a 

 vacuum, I sav the tension of its vapour will be equal to 30 x 

 (•002783313 T - 2-2637 14) 8 -- very nearly, estimated by the 

 pressure of a column of mercury in inches. 



I shall not here enter into the investigation of this theorem, 

 because it requires the previous solution of other problems on 

 which I have not yet touched, but shall proceed to give philoso- 

 phers a few specimens of its accordance with phsenomena from 

 the experiments of Mr. Robison, Mr. Southern, Mr. Dalton, and 

 Dr. Ure. 



Scholium. 



It is necessary to observe, that the constant quantities were 

 determined from Dn. Ure's' observations published in the Philoso- 

 phical Transactions for 1818. These observations are the latest, 

 and in the higher temperatures the most correct 1 believe that 

 have yet appeared; fei the lower temperatures, that is, beneath 

 212° of Fahr. they very nearly coincide with Mr. Dalton's num-r 

 bers ; a circumstance'by no means discreditable to the care and 

 skill of both, and not uncalculated to give us confidence in the 

 rest of the Doctor's results. Unfortunately for myself I have 

 neither Dr. Ure's nor Mr. Dalton's papers at hand, and cannot, 

 therefore, avail myself of their labours to push this part of my 

 inquiries, as it respects other vapours, to the length I could wish ; 

 but if ever I should write on the subject of vapours again, I hope 

 I shall have more time before me, and be better prepared to do 

 it justice. At present my object in giving this theorem is to 

 prepare the way for the solutions of one or two principal pro- 

 blems relative to the theory of the steam engine. Philosophers 

 will, in the sequel, see whether I have succeeded or not. 



Example 1. — Let the temperature be 32° Fahr. then by 

 Table 3, T = 1000, and 30 x (-002783313 T - 2-2637 14) 6 -» 

 = 30 x (-519599) 3 --. 



