— 188 — 
est point. And the variation in the adhesion between the 
solid and liquid caused by the variation in the geometric dis- 
tribution of the solid, mat and does in its turn affect the size 
of the drop. 
From this aspect one of the simplest kinds of variation is 
that offered by a system of spheres of various radii but made 
of the same matter. And this ease is an important one be- 
cause it undoubtedly offers the key to all drop-size variation 
arising from a similar cause. To study this point we may 
make use of any one convenient liquid such as water, and 
cause it to drop at a fixed rate from spheres of various radii, 
including the extreme case of a horizontal plane. 
This extreme case however presents certain practical diffi- 
culties. From a plane it is almost impossible to get a series 
of drops, uniform in growth-time and iu position. A ripe 
drop hanging from a horizontal plane of a substance which it 
wets will seek the edge thereof. Several drops may form upon 
and fall from the same plate at the same time and indepen- 
dently of one another. It is only by employing a plate not 
absolutely flat that an approximation to the required condi- 
tions can be made. Taking r for the radius of curvature there- 
fore, the first numbers for r — cc can only be considered as 
an approximation. The arrangements for the other cases 
were quite similar to that described in I Fig. III. 
No. 1. A glass plate, fastened to and held by a vertical rod. 
Nos. 2, 3, 4. Selected globular glass flasks. 
Nos. 5, 6, &c. Perfectly spherical solid glass spheres. 
