460 Prof. Tyndall on the Action of Free Molecules on 



any absorbent gas or vapour the equilibrium was destroyed, 

 the needle moved from zero; and from the observed permanent 

 deflection the absorption was calculated. Other qualities of 

 heat, and other experimental tubes than that here described, 

 were afterwards introduced into the inquiry, 



I here give the measurements executed in 1880 with the 

 vapours of nine different liquids, in experimental tubes of the 

 dimensions above given. 



Table I. 



Vapours. 



Liquids. 









Leslie's 



Leslie's 



Red-b< 





Pressures. 



cube, 



cube 



spiral 









vacuum. 



free. 





Bisulphide of carbon , 



, -48 i 



in. mer. 4 - 4 



5-0 



7-6 



Chloroform . . . . 



, -36 



jj 



12-8 



12-9 



28-8 



Benzol 



, -32 



?j 



14-8 



15-0 



44-5 



Iodide of ethyl . , 



. -36 



n 



18-4 



1U-3 



47-0 



Iodide of methyl . , 



, '46 



;> 



25-0 



26-2 



59-0 



Amylene . . . 



. -26 



W 



26-1 



27-2 



65-0 



Sulphuric ether . , 



, -28 



jj 



35-0 



35-6 



71-0 



Acetic ether . . , 



. -29 



jj 



43-3 



43-7 



77-5 



Formic ether . . 



, -36 



}) 



43-3 



44-0 



78-0 



The u pressures " in this table are chosen with a view to the 

 comparison of liquids and vapours. They express quantities 

 of vapour which are proportional to the quantities of matter 

 in the respective liquids at a common thickness. The two 

 next columns contain the absorptions per 100 of the heat from 

 two Leslie's cubes, the one with a vacuum in front of it, the 

 other placed in free air and well protected from air-currents. 

 The close agreement of the two columns proves the " front 

 chamber " to be a superfluity. It also illustrates the 1 coinci- 

 dence to be attained in these measurements when they are 

 carefully made. In the last column I have placed the absorp- 

 tions exerted by liquid layers of the respective substances at a 

 common thickness of one millimetre. The source of heat here 

 was an incandescent platinum spiral. The order of absorption 

 of liquids and vapours is the same. 



This order is, as might be expected, undisturbed when we 

 apply heat of the same quality to liquids and vapours respec- 

 tively. This is shown by the following table: — 



