194 — 
circumstances from spheres of the same size but made of dif- 
ferent material. Since, in this case, the liquid remains the 
same, Ave must limit the solids examined to such as the given 
liquid completely wets. In this case variation in the drop 
size implies a variation in the thickness of the liquid film 
covering the solid. The latter must be caused by variation 
in the adhesion between the solid and liquid. Finally such 
adhesion can only vary through one or both of two causes, 
namely variation in the density of the solid or in its specific 
adhesion dependent upon its chemical nature. 
The first qualitative experiment was made upon three equal 
spheres of Brass, Glass and Cork respectively. They were 
hung one above the other in the manner before described, so 
that the drops from one fell upon the lower one.* It was 
found that, in whatever order the spheres were arranged, 
when the flow was uniform and not quicker than gt — 2”, 
the dropping from the Cork took place with the greatest ra- 
pidity, that from the Glass next and that from the Brass 
most slowly. Showing that the brass gives rise to the largest, 
the glass to the next largest and the cork to the least drops. 
From this it would seem that the drops are in the same order 
as to size as arc the solids as to density. We shall find how- 
ever that this is not always the case : and that some other 
property as well as density is at work to influence the drop- 
size. i The quantitative experiment, the results of which are 
given in Table XI confirms the results of the qualitative ex- 
periment given above ; but shows, at the same time that the 
joint influences of density and chemical diversity of the solid 
have only a trifling effect upon the drop-size. The condi- 
tions of the experiment were similar to those previously des- 
cribed. 
* In this kind of experiment there should be a considerable mass of 
cotton wool on each sphere to receive the drops from the higher noe 
and, by acting as a reservoir, to regulate the flow- 
