Mil. \V. N. SHAW ON HYGBOMKTRIC METHODS. 129 



A. RBONAULT'S observations (with a large psychrometer) 



= e l - 0-6698 r + 0'015253 re, - 0'00522 r + 0'58299 r ' ~ - . 



B. REGNAULT'S observations (small psychrometer) 



e = e l 1-24442 T + 0'05881 T e, + 0'009006 r + 0'58299 r ^^ . 



C. Greenwich observations 



e = e l 0-27842 T 0'02309 -r e, + 0'002437 r + 0'58299 r-~ 



745 



D. KAMTZ'S observations. Psychrometer and DANIELL'S hygrometer comparison 



e = e l - 0-64569 T - 0'003861 re, + 0'012397 r + 073932 T 74 ' h . 



745 



E. KAMTZ. Chemical method and psychrometer 



e = e l 0-50051 T - 0'021641 T^ + 0-015548T 2 + Q-58299T 74 ,! 7 * . 



74o 



F. Condensation experiments 



e = e l - 0-67894 T - 0'0045928 T e l + 0'010690 T* + 0'58299 T 



G. All the observations together 



e e l 0-57515 (t tj 0'005989 (t ,) Cl 

 + 0-002664 (t - trf -f 0-58899 (t tj 



Apart from the concordance of the bai-ometric correction, there is nothiug in these 

 formulae that seems to indicate any advantage in introducing the additional constants, 

 nor does the reduction of observations, specimens of which are given, by means of 

 them, make them any more reassuring ; the differences in the pressure calculated by 

 the different formulae amount frequently to 20 per cent, of the whole, and KAMTZ 

 assigns one-sixth as the extreme error probable in using the general formulae, G. He 

 points out that the size of the bulb has some influence on the reading, and considers 

 that comparable results are only to be obtained by making comparisons between the 

 separate instruments and the condensation or the chemical method. 



To another paper by KAMTZ on the psychrometer below the freezing point, in 

 KAMTZ'S ' Repertoriura,' vol. 3, I have not been able to obtain access,* nor yet to 



* Since the above was written I have seen the paper. The chief points of it are referred to in the 

 extracts quoted from PKRNTER'S memoir (p. 137). KAMTZ proposes to add 0'5 C. to the obeerved 

 psvehrouiutric difference for ice-covered bulbs. 



MDOCCLXXXVIII. A. 



