26  G. Jonystone Stoney on the Penetration of Heat across Layers of Gas. 
heat of her smoothing-iron, and which was studied by M. Bontigny under the name 
of the spheroidal state of liquids. If a drop of water or other cold volatile liquid 
is allowed to fall into a smooth and sufficiently hot metal dish, it continues liquid 
instead of flashing off into vapour, and exhibits an appearance of great mobility. 
Here the liquid settles down upon the Crookes’s layer which envelops the metal, 
and reduces that portion which is under it to the condition of a compressed Crookes’s 
layer. Now the mechanical peculiarity of a compressed Crookes’s layer is that it 
exerts more force in the direction along which the heat travels (in the present 
instance up and down) than in the perpendicular direction; and inasmuch as 
the pressure sideways must continue to be the pressure of the atmosphere, the 
excess of pressure upwards is able to support a weight. When we also remember 
that this excess of pressure would be augmented by still further curtailing the 
Crookes’s layer, z.e., by depressing any part of the drop, we have all the mechanical 
conditions necessary for the stable equilibrium of the drop, if only the force rises to 
a sufficient amount before the drop settles down quite through the Crookes’s layer. 
This, by the theory, depends altogether on the difference of temperatures which can 
be maintained. The first thermal effect is that the drop becomes warmed by the 
radiation and penetration of heat from the hot metal below. This causes the 
liquid, if volatile, to lose heat by evaporation, and, in most cases, to lose a little 
heat also by radiation to surrounding bodies. As the temperature of the drop 
rises, the heat thus lost increases, while at the same time the heat received from 
below diminishes, and if a balance between the two is effected before the liquid 
reaches the boiling point, the drop continues liquid, the temperature remains 
henceforth unchanged, and we have before us the striking spectacle of a liquid in 
the spheroidal state. 
Addition made June 24, 1877. 
21. I have long thought it likely that the drops which may be sometimes seen 
running over the surface of a volatile liquid rest upon compressed Crookes’s layers 
intervening between them and the liquid on which they float: that they are, in 
fact, drops in the spheroidal state. Some recent observations abundantly confirm 
this suspicion. These floating globules are easily formed when a liquid as volatile 
as spirits of wine is allowed to fall in drops of a medium size from a height of 
about 8 centimetres into a vessel containing some of the same liquid moderately 
warmed, ‘They can also be occasionally produced by dropping the spirits of wine 
upon water. And everyone is familiar with them when, in some states of the 
weather, they roll about in numbers on allowing water to drip from an oar upon 
the sea. Yesterday they were abundantly produced by splashing the water of a 
neighbouring pond, and I took advantage of the opportunity to ascertain that the 
conditions required by the hypothesis were fulfilled. The temperature of the air 
was about 15°, that of the surface of the water 18° and a quarter, and a very dry 
