ADDRESS. 21 



ment of the lengtli 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 year Amontons contributed to 

 the Academy a further paper extending the scope of the inquiry. He 

 there pointed out more explicitly that as the degi'ees of heat in his 

 thermometer are registered by 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 says, will be a much greater cold than 

 what we call ' very cold,' because experiments have shown that if the 

 spring of the air at boiling-point is 73 inches, the degree of heat 

 which remains in the air when brought to the freezing-point of water is 

 still very great, for it can still maintain 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 58, the value for boiling water 

 being 73, and the zero being 52 units below the freezing-point. Thus 

 Amontons was the first to recognise that the use of air as a thermometric 

 substance led to the inference of the existence of a zero of temperature, 

 and his scale is nothing else than the absolute one we are now so familiar 

 with. It results from Amontons' experiments that the air would have no 

 spring left if it were cooled below the freezing-point of water to about 

 2^ times the temperature range whicJi separates the boiling-point and the 

 freezing-point. In other words, if we adopt the usual centessimal differ- 

 ence between these two points of temperature as 100 degrees, then the 

 zero of Amontons' air thermometer is minus 240 degrees. This is a 

 remarkable approximation to our modern value for the same point of 

 minus 273 degrees. It has to be confessed that Amontons' valuable con- 

 tributions to knowledge 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' 

 experiments and endorsed 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 

 correcting the value of the zero of the air scale to minus 270 degrees as 

 compared with Amontons' minus 240 degrees. Lambert points out that 

 the degree of temperature which is equal to zero is what one may call 

 absolute cold, and that at this temperature the volume of the air would 

 be practically nothing. In other words, the particles of the air would 

 fall together and touch each other and become dense like water ; and from 

 this it may be inferred that the gaseous condition is caused by heat. 

 Lambert says that Amontons' discoveries had found few adherents 

 because they were too beautiful and advanced for the time in which he 

 lived. 



