548 



SCIENCE. 



[N. S. Vol. XVI. No. 405. 



Aniontons contributed to the Academy a 

 further paper extending the scope of the 

 inquiry. He there pointed out more ex- 

 plicitly that as the degrees 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 ther- 

 mometer 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 boil- 

 ing-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 

 iirst to recognize that the use of air as a 

 thermometric substance led to the infer- 

 ence of the existence of a zero of tempera- 

 ture, and his scale is nothing else than the 

 absolute one we are now so familiar ^\^th. 

 It results from Amontons' experiment that 

 the air would have no spring left if it were 

 cooled below the freezing-point of water to 

 about 2i times the temperature range which 

 separates the boiling-point and the freez- 

 ing-point. In other words, if we adopt 

 the usual centennial difference 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 contributions 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 

 is not till Lambert, in his work on 'Pyro- 

 metrie' published in 1779, repeated Am- 

 ontons' experiments and endorsed his re- 

 sults that we find any further reference to 

 the absolute scale or the zero of tempera- 

 ture. 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 de- 

 gree 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 Amon- 

 tons' discoveries had found few adherents 

 because they were too beautiful and ad- 

 vanced for the time in which he lived. 



About this time a remarkable obser- 

 vation was made by Professor Braun at 

 Moscow, who, during the severe winter of 

 1759, succeeded in freezing mercury by 

 the use of a mixture of snow and nitric 

 acid. "When we remember that mercury 

 was regarded as quite a peculiar substance 

 possessed of the essential quality of fluid- 

 ity, we can easily understand the universal 

 interest created by the experiment of 

 Braun. This was accentuated by the ob- 

 servations he made on the temperature 

 given by the mercury thermometer, which 

 appeared to record a temperature as low 

 as ininus 200° C. The experiments were 

 soon repeated by Hutcliins at Hudson's 

 Bay, who conducted his work with the aid 

 of suggestions given him by Cavendish and 

 Black. The result of the new observations 

 was to show that the freezing-point of 

 mercury is only minus 40° C, the errors 



