Description of a New Hygrometer. 23 



Article IV. 



Description of a New Hygrometer ; illustrated hy experiments 

 and a comparison of its results with Sir John Leslie's, and 

 the Dew-point Hygrometers, hy John Abraham Mason, 

 M.D., Member of the Royal College of Surgeons, Edin- 

 burgh ; Extraordinary Member of the Royal Medical 

 Society, Edinburgh, Sfc. 



It has long been a subject of complaint among all prac- 

 tical meteorologists, that we have no Hygrometer which com- 

 bines the advantages of being simple in its construction, 

 easy of application, and unerring in its results. — Persons 

 unaccustomed to scientific pursuits are unwilling to devote 

 their time and attention to complex instruments, and it has 

 occurred to me that good service might be rendered to 

 Meteorology, by devising some method of ascertaining the 

 Hygrometrical condition of the atmosphere, which will 

 combine simplicity with accuracy. 



I am fully persuaded that moisture has a much greater 

 share in developing the effects of climate upon the human 

 constitution than most physicians imagine ; and I believe 

 that the following reasons have hitherto tended to impede 

 its investigation with that precision which it merits : 



1st. The uncertainty and deterioration of all Hygrome- 

 ters made of Hygroscopic substances, and their only indi- 

 cating relative differences. 



2nd. That all the Dew-point Hygrometers occupy more 

 time than most people are able to bestow upon them ; and 

 that some tact is required in their application. 



3rd. That ether of sufficient strength cannot be obtained 

 in every climate, and other chemical means of producing 

 cold cannot be always at hand. 



4th. That Sir J. Leslie's Hygrometer by evaporation is 

 considered by many to offer erroneous results, being in- 

 fluenced by radiation, currents of air, &c., and that much 

 calculation is required before the absolute quantity of hu- 

 midity can be ascertained. 



5th. That the degrees of humidity indicated by the dif- 

 ferent kinds of Hygrometers cannot be easily reduced to a 

 common standard, so as to be compared with each other. 



Now, the instrument which I propose is at once free from 



