462 Mr. G-. J. Stoney on Crookes's Layers at 



such at each point that it gives a component equal and oppo- 

 site to the resultant of the pressure of the water at that depth, 

 and of the surface-tensions round the point. Whenever the 

 Crookes's force is not quite in the direction of this resultant, 

 there will be a free tangential component ; and this must pro- 

 duce surface-currents in the water. These, however, cannot 

 be observed in the present experiment, because they are of 

 small amount, and too much mixed up with convection-currents 

 arising from the heat that reaches the water by radiation and 

 diffusion. 



When the ball is lowered until it is quite submerged, it will 

 be surrounded on all sides by an envelope of polarized air, 

 thinnest at the bottom (where the pressure of the water is 

 greatest), thickest above. So long as there is any communica- 

 tion between the polarized layer and the atmosphere, the 

 lateral stresses within the layer will be equal to P, while those 

 in the direction in which the heat penetrates will be P + p ; 

 but both of these will suffer an increase if the ball is plunged 

 deeper after the communication with the atmosphere has been 

 cut off. No one can see this splendid experiment for the first 

 time without a feeling of astonishment. 



7. A Crookes's layer formed in the same way, but without 

 the exquisite beauty which it has in this experiment, may be 

 seen any day in a smith's forge, whenever the smith has occa- 

 sion to quench white-hot iron in water. 



8. A phenomenon closely resembling the experiment with 

 the glowing ball was witnessed lately by my brother and two 

 other friends while out walking. There was a shower when 

 they reached some rather deep water. The afternoon had 

 become chilly; and the phenomenon that presented itself shows 

 that the water must have retained a temperature higher than 

 that of the air. As the rain-drops fell into the water, some of 

 them (estimated at one in twenty) became spheroidal drops 

 floating on the water ; and of these some (estimated at one in 

 six) were visibly submerged before floating about as spheroidal 

 drops. They sank, perhaps about half a centimetre, before 

 they rose to the surface, and while under water looked like 

 silvered pills, owing to the total reflection from the boundary 

 between the water and the film of polarized air which enveloped 

 each drop. 



9. Several times, in the course of this communication, I have 

 had occasion to speak of the feebleness of conduction or pene- 

 tration, compared with the rapid outpour of heat which takes 

 place on direct contact between a very hot and a cold body. 

 This is well illustrated by an experiment of M. Boutigny, in 

 which a spheroidal drop of water is formed inside a hot copper 



