NOTE ON THE SPHEROIDAL STATE. 
BY] 
W. F. BARRETT, F.r.s.£. 
[Read December 17th, 1877.] 
AT the last meeting of this Society, Mr G. Johnstone Stoney gave 
a new and beautiful explanation of the so-called spheroidal state 
of liquids, wherein he showed that the force detected by Mr. 
Crookes, and which is the cause of the motion of radiometers, was 
also competent to explain the phenomena of the spheroidal state. 
A. liquid drop is said to be in the spheroidal state when falling 
upon a hot body it does not come into contact with the surface 
but rolls over it as a flattened spheroid. A mobile elastic spring 
evidently buoys up the drop until such times as the hot body 
cools, when, with a sudden rise of temperature and generation of 
steam, the drop comes into contact with the surface below it, 
spreads out into a film, and rapidly disappears into vapour. 
Hitherto this phenomenon has been regarded as due to the 
fact that the proximity of the hot surface converts a portion of 
the liquid into vapour, the elastic force of which sustains the 
drop. There are, however, several phenomena, allied to the 
spheroidal condition, to which this generally received explanation 
gives no solution. Such, for example, as the mobility of light 
powders in a hot crucible, or the formation of globules on 
the surface of water and other liquids. Mr. Stoney’s explana- 
tion, on the other hand, embraces the whole of these outstanding 
and hitherto enigmatical phenomena. Briefly stated this theory 
is based on the fact that whenever two bodies at different 
temperatures are brought sufficiently near each other a modifica- 
tion takes place in the molecular structure of the layer of gas or 
vapour between them, giving rise to the so-called ‘Crookes’ force,’ 
wherein there is an excess of pressure in the direction joining the 
hot and cold surfaces over the pressure in transverse directions. 
Now this excess of pressure depends partly on the quantity of 
heat making its way across the intervening layer of gas or 
