Mr. T. Tate on the Laws of Evaporation and Absorption. 283 

 . Cdx Cdx C, ,d n u 



j dxu— n(n + l) — — • -$ 1 dx.x q u 



the integral sign in the first member being repeated (?» + l) times. 

 (—2) n \ xdx \xdx Sxdx . . . \ -^+ri«*= 



1 C dx.u 1 g fe.« 



1.2.3...»J x 1.1.2.3...(ra-l} J a 3 



i i 4 r ^ . u __ 



+ 1. 2*1. 2. 3. ..(11-2)* J # 5 



the integral sign in the first member being repeated (n + 1) times. 



I J J J<& * + ^ J J J& . a + 1 J J j& a 



- 1 & . m I dx . X"" 1 u. 



XL. Experimental Researches on the Laws of Evaporation and 

 Absorption. By Thomas Tate, Esq. 



[Continued from p. 135.] 



Maximum absorption of water by different substances. Measure 

 of the porosity of different substances. 



THE amount of water which a substance is capable of absorbing 

 depends upon the capacity of its pores, or the volume of its 

 interstices so far as they are permeable by water. In most 

 cases the volume of water which a substance absorbs is equal to 

 the volume of the air expelled. But this is not universally true ; 

 for I have found that water will filter through heavy sandstone 

 in opposition to an excess of atmospheric pressure. In order 

 to saturate perfectly certain substances with water, they must ba 

 boiled in a vessel exhausted of air. 



The capacity of different substances for absorbing and retain* 

 ing moisture is very various. The following substances being 



U2 



