58 Mr. G. Johnstone Stone v, 



the bottom, where the pressure of the water is greatest, thickest 

 above. So long as there is any communication 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. 



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 occasion to 

 quench white-hot iron in water. 



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. 



Several times, in the course of this communication, I have had 

 occasion to speak of the feebleness of conduction or penetration, 

 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 bottle, and 

 the neck of the bottle partially stopped by a cork through which 

 a thin tube passes. So long as the drop continues in the 

 spheroidal state, a mixture of air and vapour slowly escapes 

 through the tube in the cork, but the instant the spheroidal state 

 ceases, and the water comes into contact with the copper, a suffi- 

 cient portion of the water flashes off so suddenly into steam that 

 the cork is driven out with explosive violence. 



