210 HISTORY OF COLD AND THE ABSOLUTE ZERO. 



increased perfection of the air thermometer as a standard instru- 

 ment, Amontons's idea being to express the temperature at any locality 

 in fractions of the degree of heat of boiling water. The great nov- 

 elty of the instrument is that temperature is defined by the measure- 

 ment of the length of a column of mercury. In passing, he remarks 

 that we do not know the extreme of heat and cold, but that he has 

 given the results of experiments which establish correspondences for 

 those who wish to consider the subject. In the following 3'ear Amon- 

 tons contributed to the Academy a further pa]5er extending the scope 

 of the inquiry. He there pointed out more explicitly that as the 

 degrees of heat in his thermometer are registered b}- the height of a 

 column of mercury, which the heat is able to sustain by the spring of 

 the air, it follows that the extreme cold of the thermometer will be 

 that which reduces the air to have no power of spring. This, he saj^s, 

 will be a much greater cold than what we call "very cold," because 

 experiments have shown that if the spring of the air at ])oiling point 

 is 73 inches, the degree of heat which remains in the air when l^rought 

 to the freezing point of water is still very great, for it can still main- 

 tain the spring of 51^ inches. The greatest climatic cold on the scale 

 of units adopted by Amontons is marked 50, and the greatest summer 

 heat 5S, the value for boiling water being 73, and the zero being 52 

 units below the freezing point. Thus Amontons was the first to rec- 

 ognize that the use of air as a thermometiic substance led to the infer- 

 ence of the existence of a zero of temperature, and his scale is nothing 

 else than the absolute one we are now so familitir with. It results' from 

 Amontons's experiments that the air w ould have no spring left if it were 

 cooled below the freezing point of water to about two and one-half times 

 the temperature range which separates the T)oi]ing point and the freez- 

 ing point. In other words, if we adopt the usual centessimal difference 

 between these two points of temperature as 100^, then the zero of 

 Amontons's air thermometer is mimis 240-. This is a i'emarkal)le 

 approximation to our modern value for the same point of minus 273°. 

 It has to be confessed that Amontons's valuable contribntions to knowl- 

 edge met with that fate which has so often for a time overtaken the 

 work of too-advanced discoverers; in other words, it was simply 

 ignored, or in any case not appreciated by the scientific world either 

 of that time or half a century later. It was not till Lambert, in his 

 work on Pyrometrie, published in 1779, repeated Amontons's experi- 

 ments and indorsed his results, that we find any further reference to 

 the absolute scale or the zero of temperature. Lambert's observations 

 were made with the greatest care and refinement, and resulted in cor- 

 recting the \alue of the zero of the air scah^ to mimis 270' , as compared 

 with Amontons's miiuis 240 . Ljind)ert points out that the degree of 

 temperature which is equal to zero is what owo may call absolute cold, 

 and that at this temperature the volume of the air would l)e ])ractically 

 nothing. In other Avords, the particles of the air would fall together 



