290 Attraction of Aggregation and Chemical Affinity. 
that mercury is capable of moistening substances of greater 
or not much less specific gravity than itself, by showing that 
the angle of actual contact with them may be exceedingly 
small. 
With respect to the kind of molecular force to which the 
mathematical reasoning was intended to apply, I may observe 
that in strictness it is applicable only to that which is usually 
called the attraction of aggregation, a familiar instance of 
which, wholly independent of chemical affinity, is seen in 
water adhering to ice. I was unacquainted with Mr. Fara- 
day’s observations on this subject referred to in the note, but 
having since perused them, I quite agree with him in thinking 
that in the contact of two dissimilar substances this force is 
modified by chemical affinity, even when no chemical action 
takes place between them. There are, however, no means at 
present of estimating this effect mathematically. It is pro- 
bably greatest in the state bordering on chemical action. 
Analysis applied to the case of perfect contact caused by the 
attraction of aggregation alone, (which is a simple instance 
of the statzcs of molecular forces,) leads to the inference that 
the same fluid will rise to the same height in different capil- 
lary tubes: and Link’s experiments show, in fact, that water 
rose to the same height between glass, copper, and zinc plates ; 
sulphuric acid, between glass and copper plates; muriatic 
acid, between glass and copper; liquid caustic alkali, between 
glass and zinc; liquid ascetic* alkali (sp. gr. 17145), between 
glass and zinc. ‘The deviations from the law in the other in- 
stances may therefore be owing to chemical affinity, perhaps 
also to chemical action. The same causes would affect the 
heights of ascent of different fluids in the same tube. But I 
am disposed to think that in addition to these causes, the dif- 
ference of heights depends on the different natural conditions 
of the fluids. For instance, the most volatile fluids, which are 
probably those that are most perfectly fluid, appear by the 
experiments to rise least. A small degree of viscidity, it will 
perhaps be admitted, would tend to increase the height of 
ascent, if the condition of perfect contact be maintained. To 
separate the effect of chemical affinity from that of the attrac- 
tion of aggregation, requires experiments more numerous and 
varied than any that have hitherto been made. 
Observatory, Cambridge, March 11, 1836. 
* [Carbonated ?] 
