SCIENTIFIC SUMMAEY. 
263 
as we allow causes of error to exist in tlie domain of observatioiij which 
escape all analysis, like the physiological cause which I now introduce to the 
notice of the Academie.” 
PHYSICS. 
Laws regulating the Formation of Drops . — Those of our readers interested 
in the physics of drops have already read our abstracts of Mr. Tomlinson’s 
valuable papers upon this subject. A rival has now appeared in the field, in 
the form of the Professor of Chemistry in the Royal College, Mauritius, 
Mr. Guthrie. This gentleman has commenced his views in a memoir lately 
presented to the Royal Society, and the following are a few of the more 
important conclusions which he has drawn. The size of a drop may be 
influenced by the subjoined conditions : — 
(1.) The self-attraction and cohesion of the drop-generating liquid. 
(2.) Its adhesion to the matter upon which the drop is formed. 
(3.) The shape of the matter from which the drop moves. 
(4.) The physical relation of the medium through which the drop moves — 
on the one hand, to the liquid of which the drop is formed, and on the other 
to the matter on which it is formed. 
(5.) The attraction of the earth upon the drop-forming liquid and upon the 
medium, as influenced by their respective and relative densities, and by 
va,riation in the attracting power of the earth. 
When a drop is formed by a liquid falling intermittently through a gas, 
the following are the laws which control its bulk ; — - • 
(1.) The drop-size depends upon the rate of dropping. Generally, the 
quicker the succession of the drops the greater is the drop — the slower the 
rate, the more strictly is this the case. This law depends upon the 
difi'erence at different rates of the thickness of the film from which the 
drop falls. 
(2.) The drop-size depends upon the nature and quantity of the solid which 
■the dropping liquid holds in solution. If the liquid stands in no chemical 
relation to the solid, in general, the drop-size diminishes as the quantity 
of solid contained in the liquid increases. The cause of this seems to be that 
the stubborn cohesion of the liquid is diminished by the solid in solution. 
When one or more combinations between the liquid and the solid are 
possible, then the drop-size depends upon indeterminate data. 
(3.) The drop-size depends upon the chemical nature of the dropping 
liquid, and little or nothing upon its density. Of all liquids examined, water 
has the greatest, and acetic acid the least drop-size. Butyric acid, which has 
sensibly the same specific gravity as water, gives rise to a drop less than half 
the size of the water drop. 
(4.) The drop-size depends upon the geometric relation between the solid 
and the liquid. If the solid be spherical, the largest drops fall from the 
largest spheres. Absolute difference in radii takes a gneater effect upon 
drops formed from smaller than upon those formed from larger spheres. In 
fact, the drop increases in size according as the radius of the sphere increases 
from which the drop falls. And since the difference from this cause may 
amount to half the largest drop-size, it is worthy of the consideration of the 
