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XII. On the Natural Zero, according to FaJiretikeit's Scale. 

 Bj/ Sir George Cayley, Barf. 



To the Editors of the Philo$Oj}hical Magazine and Annals. 



Gentlemen, 



3, Rue Castiglionc, Paris, Dec. 20, 1828. 

 T SEND you the following considerations respecting the 

 ■*■ natural zero, which tlioiigh perhaps not perfectly conclu- 

 sive, yet lead to a strong probability that the point of absolute 

 privation of transferable caloric, as respects temperature, takes 

 place at ^iS degrees of Fahi-enheit's scale below his 0°, taking 

 such degrees of this scale as range between .32° and 212° as 

 the standard, and leaving the more refined inquiry as to their 

 inequality at present out of the question, though fully admit- 

 ting that the zero I have named must hereafter be regulated 

 by the final result of that inquiry. 



It appears that hydrogen gas at a mean temperature is about 

 11,242 times lighter than water, and also that it can exist as a 

 component part of water : hence if it were mechanically con- 

 densed 448 times, when of the temperature of 32°, and sup- 

 posing the particles to be as dense as water, there would still 

 remain twenty-two-fold more space unoccupied than occupied 

 by them; hence there would be no reason to suspect that their 

 chemical relation to each other would be altered or deranged 

 by this condensation. If 10,000 cubic inches of hydrogen gas 

 under mean atmospheric pressure at a temperature of 32°, be 

 elevated to the temperature of 212°, it will be expanded to 

 13,744 cubic inches, and all the experiments that have been 

 made on the subject prove, that the expansion or contraction 

 of all the gases at a temperature of 32° proceed in perfect uni- 

 formity with the addition or privation of caloric as measured 

 by the thermometer, giving one 480th part of the whole bulk 

 for each degree of Fahrenheit's scale. As this is the property 

 of all the permanent gases, differing so widely as they do in 

 their specific gi-avities, chemical qualities, and in their specific 

 relation even to caloric itself, it seems to point out that in these 

 aeriform fluids, when chemical attraction is in their own na- 

 ture overcome, the expansion becomes the actual measure of 

 the transferable caloric they contain, in that relation to heat 

 we call temperature. In all these gases if we could reduce 

 the temperature 480° below 32°, all bulk, as connected with 

 temperature, would cease ; the particles would become conti- 

 guous, and deprived of all elasticity. The effect seems the 

 measure of the cause ; they originate and cease together. It 

 may be argued against this theorv, that steam and the vapours 



of 



