454 delations of Air, Heat, and Cold. 



paint, to facilitate their discharge of heat. For the same 

 reason, metalHc pots are more easily heated on the fire, 

 after their bottoms have become tarnished or smckcd. If 

 a bright surface of metal be slightly furrowed or divided by 

 fine flutings, it will emit heat sensibly faster, because the 

 prominent ridges, thus brought closer to the general at- 

 mospheric boundary, will excite the pulsations with aug- 

 mented energy. 



" On the other hand, a plate of metal, however thin, if 

 only burnished on each side, will form the most efficacious 

 screen. A smooth sheet of pasteboard, gilt over both sides, 

 would answer the same purpose. But a complete and ele- 

 gant screen might be composed of two parallel sheets of 

 China paper, placed about an inch asunder, and having 

 their inner surfaces gilt, and their outsides sprinkled with 

 flowers of gold and sdver. 



'* Since, in a still atmosphere, the momentary flow of 

 heat from any vessel, whatever tiiis may contain, depends 

 merely on the condition of its surface, the whole accumu- 

 lated discharge, during similar descents of temperature, is 

 evidently proportional to the time elapsed. Hence a very 

 simple and accurate method is sus2;estcd, for ascertaining 

 the capacity of different liquids or their specific attraction 

 to heat. Into a glass ball, two or more inches in diameter 

 and blown extremely thin, wiih a narrow short neck, and 

 having a delicate thermometer inserted through it, the liquid 

 to be exammed, which had been previously warmed a few 

 degrees, is carefully introduced by means uf a funnel. The 

 ball is then made to rest against the tapering points of three 

 slender glass rods at the height of several inches above the 

 table, and sheltered from any irregular agitation of the air 

 of the apartment by a large receiver passed over it. The 

 number of seconds which the thermometer now takes to 

 sink from one given point to another, or to the middle of 

 its distance from the limiting temperature, is noted by help 

 of a stop-watch ; and the ball being thoroughly emptied 

 and again successively filled with other liquids, the like ob- 

 servations are repeated. These several intervals of time, 

 allowing a slight correction for the matter of the shell it- 

 self and of the inserted bulb of the ihermomeier, will con- 

 sequently express the proportional quantities of heat con- 

 tained in equal bulks of the successive liquids. But their 

 densities being already known, it is hence easy to c(;m- 

 pute their respective capacities, or the quantities of heat 

 which equal weights of them are capable of containing. 

 By a process grounded on the same principles, the capacity 



of 



