Hydrhophic Substances of an Animal and Vegetable origin. 241 
tracted attention, first by themselves, and then in connection 
with other fluids. A number of like portions of the same sub- 
stance were subjected to experiment ; and, by taking the mean 
result, the cohesive force, &c. were pretty accurately determined. 
The same number of similar portions were then subjected to the 
action of various fluids, and the resulting loss of cohesion, in- 
crease of volume, &c. were determined, in each case, after the 
same method. It was found that, in certain cases, in those sub- 
stances which had been immersed or soaked in oil, the cohesive 
force was not nearly so much reduced as when other fluids were 
applied to them ; and hence I was led to try the effects of other 
fluids on those bodies that had been previously well soaked in 
oil. The result of this experiment was, that previous immer- 
sion in oil had but a small effect in preventing, or, speaking more 
correctly, in retarding, the absorption of water in the state of a 
liquid. 
Having procured four highly sensible hygrometers, two of 
which were made of a vegetable, and the other two of an ani- 
mal substance, I immersed the sentient part of one of each kind 
in oil. After they had thus been completely saturated, and the 
oil adhering to their surfaces had been gently wiped off, by 
means of a soft hair pencil, it was observed that no degree of 
expansion had been produced by the fluid, as the indices re- 
mained stationary at the degree to which they pointed, previous 
to the application of the oil. 
The four hygrometers, that is, two that had been oiled, and 
two that were free of that fluid, were now placed in a body of 
damp air. The result of this experiment, which has, since that 
time, been often varied and repeated, was, that previous immer- 
sion in oil, so as to render an opaque substance almost perfectly 
transparent, had no effect in preventing, and so little in retard- 
ing, the absorption of aqueous vapour from the atmospheric air, 
as to be almost imperceptible. When an oiled instrument, and 
one that is free of oil, are removed from very dry air into air 
that is very damp, the motion of the former may be more regu- 
lar and steady than that of the latter ; but this constitutes all the 
apparent difference. 
This curious result was certainly not anticipated. It seems, 
however, to warrant the conclusion, that oils only enter into and 
