NOTE ON THE SPHEROIDAL STATE. 



BT 



W. F. BARRETT, f.r.s.e. 

 [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 



