182 NATURE AND LIFE. 
stances, solid or fluid, placed on moistened glass, or in a 
saucerful of water, instantly act on those molecules of the 
liquid which they touch, and repel them more or less, pro- 
ducing a vacuum. He judged that this method might 
serve to make odors sensible to sight, and enable us to dis- 
tinguish odorous from inodorous bodies. These move- 
ments of odorous bodies on the surfaces of liquids, of 
which camphor particularly gives so curious an instance, 
have lately been studied with the greatest care by a French 
physiologist, with a view to establishing a theory of odors. 
With this purpose Liégeois has examined most of the 
odoriferous substances, and has ascertained that almost 
all of them perform various motions of circulation and dis- 
placement on the surface of water, resembling those noted 
with camphor. Some act precisely as camphor does. 
Among these are benzoic acid, succinic acid, the rind of 
bitter oranges, etc. With others, motion soon stops, for 
they are quickly surrounded by an oily film which keeps 
them confined. Some must be reduced to powder before 
the phenomenon takes place. As regards odorous liquids, 
it occurred to Liégeois to saturate very light and spongy 
seeds, themselves odorless, with them, and he then found, 
on throwing the seeds on water, that circulatory and dis- 
placing movements took place, as with other substances. 
He concluded, from a series of experiments methodically 
tried, that the motions in question must be attributed, not 
to a release of gas, acting in the manner of a recoil, but sim- 
ply to the separation and rapid diffusion, within the water, 
of the odorous particles. The volatility of substances can- 
not be admitted to have any part in explaining the phe- 
nomenon. It depends wholly on the affinity of fluids for 
the odorous particles, and also for those of fatty matter. 
Liégeois found, for instance, that a drop of oil put on the 
surface of water, without sensibly lessening in size, emits 
an enormous quantity of microscopic droplets, which are 

