Experimental Inquiries respecting Heat and Vapor. 305 
ced over an argand spirit lamp. These portions were not of suffi- 
cient amount or frequency to prevent the increase of temperature in 
the metal, and consequently the times of vaporization were diminish- 
ed to a certain point, after which they were observed to increase. 
The temperature had then reached the point where repulsion begins. 
The temperature at the moment when the point of repulsion appear- 
ed to have been attained was noted, and the experiments continued 
until an unequivocal increase in the time of evaporating the unit of 
water was observed. ‘The lamp being now withdrawn, the tempera- 
lure was allowed to descend, and the rapidity of vaporization was of 
course augmented ; still lowering the temperature, the point of great- 
est action was passed, and the production of steam became slower 
from want of sufficient heat. 
By thus reversing the temperatures, and alternately passing and 
repassing the point of most vigorous action, the limits of that action 
were determined to a certain degree of exactness. It soon became 
evident, that it was far below the boiling point of mercury, and con- 
siderably above that of water boiling in open air. It was not diffi- 
cult to ascertain too, that the range of most rapid action lay between 
300° and 350°. In order to vary the mode of experimenting, and, 
atthe same time, to give more exact indications in several particu- 
lars, the second method, above referred to, was devised. This con- 
sisted in employing a bar of iron, about 14 inches long, 1,’ wide, 
and 1, thick. -A number of cylindrical holes, half an inch in diam- 
eter, and one inch apart, (from centre to centre,) were bored along 
one of the sides, extending nearly through the thickness of the bar. 
Adjacent to each of these holes, which were five in number, were 
sunk small conical cavities, ;3, of an inch deep and /; of an inch in 
diameter at top, forming basins or cups to receive drops or other 
small measured portions of liquids. ‘The cylindrical holes were to 
teceive mercury, into which the bulbs of thermometers could be 
plnged, to ascertain the temperature of the part of the bar and of 
cup opposite. The thermometers were supported from above, 
byhooks bent over the bar and placed in proper positions to allow 
the bulbs to descend just far enough to be completely immersed in 
the reservoir of mercury, but not to carry the centre of the bulb 
low the level of the bottom of the contiguous cup. 
y this means the temperature of the mercury was measured, at 
4 point where it must have been the same as that of the generating 
surface. The five receptacles of mercury were placed near the 
Yet. XX1.—No. 2. 39 
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