Chemistry and Physics. 261 
gas, the penny of temperature produced by the ria ee - 
stresses to elastic solids which you have investigated experi 
a and the cooling effect I have proved to be produced b pene 
ing out a liquid film which I shall have to notice particularly 
below? Easy enough experiments on the contact electricity of 
metals will answer this eM If the — erence re 
r i 
and copper, consequent on mutual approach with temperature kept 
constant, will be greater, and on the latter supposition less, than I 
have osehinatiod’ above. Till the requisite experiments are made, 
further speculation on this subject is profitless; but whatever be 
the result, it Pei invalidate the conclusion that a stratum of 
esas entimeter thick cannot contain in its ariel 
many, if so del as one, molecular constituent of the Be- 
sides hte two reasons for limiting ek smallness of statin or eae 
cules which I have now stated, two others are afforded by the 
lies. of capillary attraction, and Claasius? and Maxwell’s mag- 
nificent working out of the Kinetic Theory of gases. e 
that of a water bubble, I rs ae (as you may vorty seats} that 
a quantity of water extende @ thmness Of .-.,+-5.+ of a cen- 
.timeter would, if its tension eased constant, have more ener. 
than the same mass of Mee in ee condition by tags hy 100 
times as much as suffices to it by 1° Ce ah. This is more 
Cae, (Pece. Am. Phil. ca xi, 313, ant e tyes 
of different mechanical equivalents will o open a new field for inves- 
tigation, which may prove to be fertile in valuable results. 
* Proceedings of the Royal Society for April, 1858. 
