HIvSTORY OF COLD AND THE ABSOLUTE ZERO. 211 



aiul touch viivh other :iiul hrcoinc chaise like >viit(M', aiul from this it 

 niiiy he inferred that the gaseous condition is caused by heat. Lam- 

 bert says that Amontons' discoveries had found fcAV adherents, ])ecause 

 the}' were too beautiful and advanced for the time in which he lived. 

 About this time a remarka])le observation was made by Professor 

 Braun at Moscow, who, during the severe winter of 17;>'.), succeeded 

 in freezing men-ury ])y the use of a mixture of snow and nitric acid. 

 A^^len we remember that mercury Avas regarded as (|uite a peculiar 

 substance possessed of the essential (quality of fluidity, wo can easily 

 understand the universal interest created by the experiment of Braun. 

 This was accentuated by the ol)ser^'ations he made on the temperature 

 gi\'en by the mercury tluM'mometer, whicli appeared to record a 

 temperature as low as miiuis 200^ 0. The experiments were soon 

 repeated b}' Plutchins at Hudson Bay, who conducted his work with 

 the aid of sugg-estions gi\'en him l)v Cavendish and Black. The result 

 of the new observations was to show that the freezing point of mer- 

 cury is onh' minus -iO"' C, the errors in former experiments having 

 been due to the great contraction of the mercury in the thermometer 

 in passing into the solid state. From this it followed that the enor- 

 mous natural and artiticial colds which had generally been believed in 

 had no proved existence. Still the possible existence of a zero of tem- 

 perature very different from that deduced from gas thermometry had 

 the supi)ort of such distinguished names as those of Laplace and 

 Lavoisier. In their great memoir on Heat, after making- what they 

 consider reasonable hypotheses as to the relation l)etween specific heat 

 and total heat, they calculate values for the zero which range from 

 1,5()(» to ;;,()(I0 below melting ice. On the whole, the^^ regard the 

 absolute zero as l)eing in any case 600° below the freezing point. 

 Lavoisier, in his Elements of Ch(Miiistrv. published in 1702, g-oes fur- 

 ther in the direction of indefinitely lowering the zero of temperature 

 when he says: 



'"We are still very far from being al)le to produce the degree of 

 a])solute cold, or total deprivation of heat, being unacquainted with 

 any degree of coldness Avhicli we can not suppose capable of still fur- 

 ther augmentation; hence it follows we are incapable of , causing- the 

 ultimate particles of bodies to approach each other as near as possible, 

 and thus these particles dt) not touch each other in any state hitherto 

 known.'' 



Even as late as the beginning- of the nineteenth century we find Dal- 

 ton, in his new system of Chemical Philosophy, giving- ten calculations 

 of this value, and adopting finall}' as the natural zero of temperature 

 minus 3,000- C. 



In Black's lectures we find that he takes a very cautious view with 

 regard to the z(n-o of temperature, but as usual is admirably chnir with 

 regard to its exposition. Thus he says: 



''AVe are ignorant of the lowest possible degree or l)eginning of 

 heat. Some ingenious attempts haxe been made to estimate what it 



