T H E 



PHILOSOPHICAL MAGAZINE 

 AND JOURNAL. 



31^' AUG UST 1822. 



XVI On the Hygrometer by Evaporation. Bij J. Ivory, 

 M.A. F.R.S. 

 To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



1 The idea of employing the evaporating power of the 

 atrnosphere for discovering its condition in regard to moisture, 

 tsTeVo the late most ingenious philosopher Dr. James Huo^^ 

 of Edinburgh. He dipped a thermometer m -^ter, bori. bemg 

 previously brought to the general temperature and then ex 

 noslicr the wet bulb to a cSrrent of air, lie marked how many 

 Si tL mercury sm.k in the tube; and he estima ed the 

 d ^ess of the air bj the quantity ^^ ^he dq.ress.om 1 u-^ 

 certainly a very curious experiment; and it we go back to the 

 thne at which it was made, before 1792, it -f l-JjP^,^j^^j f^ 

 xnitted that no accurate and complete ^J^ ,«""t^ot it couU the^^^ 

 be mven for want of a sufficient knowledge ot the law. that 

 obJi; between permanent elastic fluids and the vapours niixed 

 with them. The experiment is deserving ot d .cu.sion ch a j 

 hi two respects— Is the degree of the depression of tlie thei- 

 rrteTCndent only on the f^^^J^^J^JZ 

 atmosphere, without being aflected ^^ .^^X^"^^^^^ 

 «tnnrps? What is the re ation between the depie.sion oi ine 

 rrm'meteVand the tension of the aqueous vapour diflused lu 



^'VSr Wie, of Edmburgh, has aeterniin^ that U;e 



cold produced in Dr. Button's experiment ^^^^f^ ^ 'f,f. 



to the drying quality of the ^^^^^^T^lXCr i very 

 flueuced by any other circumstances; and app jni J 



SSte iiLuLnt, his df-^^f !^-::;niJ:e v;rx 



the degree of depression, he has '^""^^^ '"^^^'' .''^^ „ , ,Y ..,.ars 

 that bfars his name. This instrument ^ ^^^^^ 'J^^ ; Hs 

 befbre the public, and it ';-^,'^-';S ' o j o miuir^any 

 learned inventor, in many d.lleu-m »"' " ; ;,ii,,,. c).i the 

 further development of ''^P'"-;;;';^;; jS^r \han to dis- 

 present occasion our mlenl.on jcacho no h in 

 cuss the original oxperin.ent n.adc by D. . I luttou. ^ ^^,^ 



Vol. GO. No. 2y.'. Aui;. \WL 



