532 HISTORY OF SCIENCE. 



companied by a great absorption of heat, and water in a cylindrical 

 vessel c put in the hollow part of D is quickly frozen. This action is 

 explained on the dynamical theory of heat by the transference of the 

 molecular motions of the vessel D and its contents to the particles of 

 the liquid ammonia in their passage to the gaseous state. The par- 

 ticles of bodies at all temperatures above -273 Cent, are supposed to 

 be in constant movement with greater or less velocity according to 

 their temperature. It is their loss of movement by the impulses taken 

 up by the ammonia particles that gives rise to the effects we denomi- 

 nate cold. 



FIG. 246. 



A singular class of phenomena connected with the vaporization of 

 liquids was made known by LEIDENFROST, and in 1843 was further 

 illustrated by BOUTIGNY, who supposed that they were due to some 

 .hitherto unrecognized condition that liquids were capable of assuming, 

 and denominated by him the Spheroidal btate. If a silver vessel be 

 treated as represented in Fig. 247, and a drop of water from a pipette 

 be allowed to descend upon it, the drop will not flash into steam, and 

 will not touch the metal, but will glide over its surface like a drop of 

 dew on a cabbage-leaf. In fact, an attentive observation will reveal 

 to the eye a distinct interval between the drop and the hot metal. 

 When water is dropped into a nearly red-hot silver dish, a considerable 

 quantity may be introduced without the liquid wetting the dish or 



