Manchester Memoirs, Vol. Ixv. (1921), No. 3 3 



admit a temperature limit on the ascending side ; that is, we 

 can hardly think of any given temperature which could not 

 be exceeded under quite conceivable circumstances. We 

 know, for example, that any metal — say, platinum — may be 

 melted if its temperature be sufficiently increased ; that a 

 further sufficient increase will convert the liquid metal to the 

 gaseous state, and that the gaseous metal may be heated 

 indefinitely while in that state. We know the behaviour and 

 properties of many substances at high temperatures, and are 

 aware of the strong tendency of all chemical compounds,, 

 when highly heated, to split up into the elementary bodies 

 composing them. All this we appreciate, but we find it 

 difficult to see how a point of temperature could be reached 

 when it could be said : this is a physical limiting point on 

 the ascending scale ; we may heat a substance up to this 

 temperature but not beyond. It is necessary here to distin- 

 guish between a conceivable limit and a practical limit under 

 existing conditions. We may thus place limits, say, to the 

 maximum temperatures of coal gas and air explosions, or the 

 temperatures possible from the electric arc ; the limit with 

 coal gas and air depending on one set of conditions and the 

 electric arc upon another set, such as the vaporising point of 

 carbon, and so on. In the same way, at the middle of last 

 century, it would have been considered quite reasonable to 

 suppose that human existence was carried on at an inter- 

 mediate plane of temperature, and that temperatures might 

 exist as low relatively as our known furnace and combustion 

 temperatures are high. At this time such an idea was quite 

 a reasonable one. It is remarkable that, notwithstanding all 

 the difficulties in the way, Joule in 1847 and Thomson in 1848 

 proposed temperature scales involving the idea of absolute 

 zero. Joule based his proposal on the dynamic theory of the 

 nature of a gas, and using the centigrade thermometer degrees 

 he concluded that the whole motion of the gas particles or 

 molecules would be exhausted when the gas reached the 

 temperature of -273°C. Obviously if heat be caused by the 

 motions of molecules of matter, when the motion ceases the 

 body is totally deprived of heat — it has reached the absolute 

 zero of temperature. As Joule had arrived at the mechanical 

 theorv of heat by laborious experiments, begun in 1838, and 

 had fully proved the correctness of the theory and made 

 accurate quantitative determinations of the mechanical value 

 of heat in foot lbs., from 1843 to 1848, he was justified in 

 proposing this limit. Thomson, however, in the next year, 

 reasoning from the Carnot cycle, also attempted to deduce 



