396 Experimental Researches on the Depressions [July, 



V. — Experimental Researches on the Depressions of the Wet-bulb Hygro- 

 meter. By James Prinsep, F. R. S. Sec. As. Soc. 



At the first meeting of the British Association for the advancement 

 6f Science, the Committee appointed to draw up a list of desiderata 

 in the various departments of science, included among the objects of 

 meteorological inquiry an investigation of the theory of the wet-bulb 

 hygrometer : and in the circular then prepared, and at the subsequent 

 annual meetings repeated, the Meteorological Committee was pleas- 

 ed to compliment with its favourable notice the papers published 

 anonymously on this subject in the Calcutta " Gleanings in Science." 

 The requisition of the British Association appears to have remained 

 unanswered until the Dublin meeting in August last, when Professor 

 Apjohn, of the Royal College of Surgeons in Dublin, brought forward 

 the results of his own experiments, and expounded a simple and elegant 

 formula which he had in every case found to agree with them, and 

 to be practically applicable to the various conditions of the problem. 

 Dr. Apjohn's papers are published in the Philosophical Magazine 

 for March, October and December, 1 835 ; and it is principally an obser- 

 vation in the opening of his memoir which induces me to revert to 

 the subject. " In the first report," he says, " mention is made of a 

 register of observations kept in the East Indies, which, as belonging 

 to high temperatures, would necessarily exhibit great depressions, and 

 would therefore be valuable as a standard of comparison ; but I have 

 in vain searched for the Calcutta Journal ' Gleanings in Science,' in 

 which they are said to be contained." 



In one respect we may deem it fortunate that the sluggish circular 

 tion of our humble periodical had not attained the shores of Ireland ; 

 if to the want of the data which " the Gleanings" might have fur- 

 nished we are indebted for the series of experiments undertaken by 

 Dr. Apjohn ; for the more varied these may be, and the more numer- 

 ous the observers, the more confidence may reasonably be placed in 

 any formula that may accommodate itself to the whole. 



I might without vanity claim to my own share as large a portion of 

 the labour of experimental investigation as has rewarded the patience of 

 any observer of the wet-bulb indications ; having, with little intermis- 

 sion, registered daily observations since 1822 ; but 1 am more anxious 

 to claim for my lamented fellow labourer, Captain Herbert, the merit 

 of having treated the theoretical portion of the subject — I will not say- 

 in a more philosophical manner than had hitherto been followed, 

 because Gay Lussac had before exercised his masterly hand upon it, 

 but, — in a manner equally sound in principle and creditable to himself, 



