HEAT. 



temperature while in that situation, he 

 regarded this as a proof that heat is 

 material, on account of its capability of 

 passing through a vacuum. 



Count Rumford proved the. passage 

 of heat through a. Torricellian vacuum, 

 that is, the space left at the top of a ba- 

 rometer by the mercury falling. He 

 placed a thermometer in such a va- 

 cuum, and submitting the whole appa- 

 ratus to changes of temperature, the 

 thermometer was affected by every 

 change. The Count imagined that -the 

 very subtile vapour which arises from 

 quicksilver, and occupies the space 

 called the Torricellian vacuum, is too 

 rare to transmit caloric by its vibrations 

 in a short time ; and concluded, there- 

 fore, that heat being able to pass through 

 such a space, without the aid of any 

 vibrating elastic fluid, must be material. 



The strongest argument in favour of 

 the material nature of heat is probably 

 that which is derived from its radiation. 

 "When a heated body is exposed in the 

 atmosphere, a portion of its heat gra- 

 dually quits it, and passes rapidly 

 through space in straight lines : this 

 heat may be reflected by mirrors and 

 condensed by lenses ; and always pro- 

 duces effects upon bodies exposed to its 

 influence. 



Attempts were made by Buffon, Roe- 

 buck, and Whitehurst, to ascertain if 

 the weight of bodies, to which heat 

 is applied, is increased : but their expe- 

 riments have been considered deficient 

 in philosophical accuracy. 



A very remarkable result was obtained 

 by Dr. Fordyce in an experiment to 

 determine the weight of latent heat, 

 described in the 75th vol. of the Philo- 

 sophical Transactions. He put about 

 1700 grains of water into a glass globe, 

 three inches in diameter, and sealed it 

 hermetically; it then weighed 2150fi 

 grains ; its temperature having been 

 reduced to 32 by being plunged in a 

 freezing mixture. When its weight was 

 ascertained, it was again submitted to 

 the freezing mixture for twenty minutes, 

 until a part of the water was frozen. 

 Its weight was ascertained, after it had 

 been very carefully dried, and it was 

 found to have gained ? ' s th part of a 

 grain. 



This process was repeated five times, 

 more of the wr.ter being frozen each 

 time, and an increase of weight obtained. 

 "When all the water had become solid, 

 the weight gained was T 8 , of a grain ; 

 the temperature of the globe and the ice 



which it contained having been reduced 

 to 12 of 'Fahrenheit's scale. The beam 

 used was a very delicate one, and the 

 temperature of the room during the ex- 

 periment was 37. 



Similar experiments were made by 

 Morveau and Chausier, with similar re- 

 sults ; sealed glass vessels containing 

 water becoming heavier when they were 

 frozen. In one experiment, two pounds 

 of sulphuric acid lost three grains of 

 its weight when it became fluid, after 

 having been frozen. 



Were the results of these experiments 

 satisfactorily established, they would 

 prove that bodies become heavier on 

 the discharge of caloric ; and conse- 

 quently, that the combination of caloric 

 with a body renders it lighter. 



A fallacy in determining the results of 

 these experiments may be ascribed to 

 overlooking the fact, that the air above 

 the scale being cooled down, by the 

 frozen body in it, to a lower degree than 

 the other parts of the atmosphere of 

 the room, that portion of it below the 

 scale would necessarily be displaced, 

 and the scale preponderate. But other 

 philosophers have tried experiments of 

 the same kind, without obtaining cor- 

 responding results. 



The weight of frozen and liquid sul- 

 phuric acid was tried by Fontana, with- 

 out finding any difference. 



Lavoisier took a thin glass flask con- 

 taining a pound of water, and having 

 hermetically sealed it, weighed it very 

 accurately, and then submitted it to 

 the usual cooling process, by which 

 the water was frozen; but the flask 

 weighed exactly the same when its con- 

 tents were solid as when they were fluid. 

 In another experiment the same philo- 

 sopher put six grains of phosphorus 

 upon a small capsule, within a very 

 strong glass flask, which he closed se- 

 curely ; he then weighed it, with great 

 care, and afterwards inflamed the phos- 

 phorus, by directing upon it the rays 

 of the sun through a burning glass. 

 No difference of weight was discovered 

 when the vessel was weighed again after 

 becoming cold ; nof, indeed, could any 

 be expected from such an experiment. 



Count Rumford made an experiment 

 which seemed to confirm the result 

 obtained by Dr. Fordyce and others ; 

 but on varying the same experiment, 

 he concluded differently. He put equal 

 weights of water and quicksilver into 

 two bottles, very much alike, and susr 

 pended them to the arms of a deli- 



