these experiments is this, that the heat 

 produced was greatest at the first stroke 

 to which each piece was subjected, less 

 at the second, and less still at the third. 

 After the third stroke, the temperature 

 was but very little raised. The follow- 

 ing numbers are the degrees of heat ac- 

 cording to the Centigrade scale which 

 the strokes of the press occasioned in 

 two pieces of copper. 



C First Piece 

 "[Second Piece 



(First Piece 

 2nd Stroke { Second Piece 



( First Piece 

 \ Second Piece 



1st Stroke 



3rd Stroke 



9.60 

 11.56 

 4.06 

 2.09 

 1.06 

 0.81 



The other metals gave similar re- 

 sults. 



The quantities of heat here measured 

 by the Centigrade scale, may easily be 

 estimated according to the scale of 

 Fahrenheit, on recollecting that one 

 degree of the former is equal to one 

 eight-tenths of the latter, or that 10 

 of the Centigrade scale are equal to 18 

 of Fahrenheit, 



It appears, therefore, from these ex- 



Seriments, that the degree of heat pro- 

 uced is always in proportion to the 

 degree of condensation. The specific 

 gravity of a piece of copper before the 

 first stroke was 8.8529, after it 8.8898 ; 

 and after the second stroke 8. 9081. 

 The specific gravity of silver before the 

 operation was 10.4667, and after it 

 10.4838. 



The other hypothesis which has pre- 

 vailed with regard to the cause of heat 

 is, that it consists in motion among the 

 particles of bodies. 



The invention of this hypothesis is 

 usually ascribed to Lord Bacon, who 

 having observed, in some instances, a 

 connexion between rise of temperature 

 and increase of motion, concluded that 

 motion is always the cause of rise of 

 temperature, or, as expressed by him- 

 self, that "heat arises from violent mo- 

 tion in the internal parts of bodies." 

 This hypothesis was adopted by Boyle, 

 and the opinions which Newton main- 

 tained also corresponded with it. 

 He believed " that heat consists in a 

 minute vibratory motion in the particles 

 of bodies, and that this motion is com- 

 municated through an apparent vacuum, 

 by the undulations of a very subtile 

 elastic medium, which is also concerned 

 in the phenomena of light." 



The production of heat by friction 



HEAT. 



is known to some of the least- civilized 

 races of men, who light their fires by 

 rubbing two pieces of wood together. It 

 has been considered as furnishing the 

 strongest argument against the mate- 

 riality of heat ; and consequently in 

 favour of the hypothesis of motion. 



It occurred to Count Rumford, who 

 had observed the great heat produced in 

 the operation of boring cannon, that the 

 heat occasioned by friction might be 

 ascertained by a similar process. He 

 took an unbored cannon, with the large 

 projecting piece " two feet beyond its 

 muzzle," which is usually cast with 

 cannon to ensure solidity: this pro- 

 jecting piece was bored, and reduced to 

 the form of a hollow cylinder, attached 

 to the cannon by a small neck : the 

 whole apparatus being wrapped in 

 flannel, was made to revolve upon its 

 axis by the power of horses, and a blunt 

 steel borer was pressed against the bot- 

 tom of the cylinder. The whole mass 

 of metal at the commencement of the 

 operation being at the temperature of 

 6 0, the force with which the borer was 

 pressed against the cylinder was esti- 

 mated at about 10,000 pounds avoirdu- 

 pois, and the surface of contact between 

 the borer and the bottom of the 

 cylinder was about two square inches. 

 The cylinder had made 960 turns in 

 half an hour ; the apparatus was then 

 stopped, and the heat which had been 

 produced ascertained, by introducing a 

 mercurial thermometer into a perfora- 

 tion of the cylinder extending from the 

 circumference to the axis, by which it 

 was found that its temperature was 

 raised to 130, which was considered to 

 be a correct indication of the mean 

 temperature of the cylinder. The par- 

 ticles of iron abraded during the opera- 

 tion weighed 837 grains, being about 

 s^th part of the whole weight of the 

 cylinder. 



The experiment was varied by the 

 same philosopher. He fixed a cylinder 

 of brass, partly bored, in a box contain- 

 ing eighteen pounds of water, excluding 

 the water from the bore of the cylinder 

 by oiled leathers. The borer was made 

 to revolve, by machinery, thirty-two 

 times in a minute. The temperature, 

 which at the commencement was 60, 

 rose in an hour to 107; and in two 

 hours and a half the water boiled. The 

 whole apparatus, weighing fifteen, 

 pounds, was raised to the same tem- 

 perature. In estimating the quantity 

 of heat produced in this experiment, 



