Experimental Inquiries respecting Heat and Vapor. 309 



appeared to proceed, in part, from the obstruction which the paper 

 opposed to the rotation of the circle of water. When a very small 

 circle of paper, or any other Hght body, was placed upon the surface, 

 it soon acquired the motion of the fluid, and the exceeding velocity 

 of the latter became manifest to the eye. The rotary motion is not 

 however the uniform result of such experiments. 



There will often be seen a scalloped figure with a greater or less 

 number of re-entering curves, destroyed and reproduced with aston- 

 ishing rapidity and regularity. A slight humming noise was also oc- 

 casionally perceived, as the liquid was alternately raised and depress- 

 ed by this species of movement. Gravity was here put in equilibrium 

 with the repulsive force of caloric, and as the equihbrium must from 

 the nature of the fluid be unstable, there was a constant effort of those 

 parts of the fluid which happened for a time to be less resisted than 

 others by the heat, to obey gravity and come nearer the surface ; but 

 as they descended they came to be, in turn, more vigorously resisted, 

 and sent up again with energy, even beyond the distance of equilibri- 

 um. A new descent was the consequence, and the alternation once 

 established, was easily maintained by the momentum of the fluid and 

 the perfect elasticity of the spring on which it constantly impinged. 

 This phenomenon is similar in character, and probably admits a sim- 

 ilar explanation to that of an experiment of Mr. Faraday, in which a 

 segment of a cylinder of metal has a narrow groove cut longitudinal- 

 ly along the convex side, forming two straight edges one or two 

 tenths of an inch asunder. If this segment, heated to four or five 

 hundred degrees, is laid on another polished metallic plane surface, 

 so as to rest upon the two edges, it will soon acquire a rapid oscilla- 

 tory motion, bringing the two edges alternately in contact with the 

 plane below. This oscillation may be sufficiently rapid to cause a 

 ringing or humming noise. In this case the radiation is from the os- 

 cillating body downwards, while in that of a fluid undergoing evapo- 

 ration, it is from the fixed plane to the oscillating body or liquid up- 

 wards. 



The temperature of the liquid while resting over the red hot sur- 

 face of iron, was found to be 210°. 



4. The resistance to actual contact, which is furnished by heat in both 

 the cases just mentioned, is exemplified in many processes of art. 

 The attempt to perforate a bar of hot iron with a cold steel hit, will 

 present a sensible illustration of this point. The resistance may how- 

 ever, by mechanical pressure, be overcome to such an extent as to 



