OCTOBKE 3, 1902.] 



SCIENCE. 



551 



although it is unattainable, for the same 

 reason we ought to accept the reality of the 

 absolute zero. We know now that Gay- 

 Lussae was wrong in supposing the incre- 

 ment of temperature arising from a given 

 gaseous compression would produce a cor- 

 r^ponding decrement from an identical 

 expansion. After this time the zero of 

 temperature was generally recognized as a 

 fixed ideal point, but in order to show that 

 it was hypothetical a distinction was drawn 

 between the use of the expressions, zero 

 of absolute temperature and the absolute 

 zero. 



The whole question took an entirely new 

 form when Lord Kelvin, in 1848, after the 

 mechanical equivalent of heat had been 

 determined by Joule, drew attention to 

 the great principles underlying Carnot's 

 work on the 'Motive Power of Heat,' and 

 applied them to an absolute method of 

 temperature measurement, which is com- 

 pletely independent of the properties of 

 any particular substance. The principle 

 was that for a difference of one degree on 

 this scale, between the temperatures of the 

 source and refrigerator, perfect engine 

 should give the same amount of work in 

 every part of the scale. Taking the same 

 fixed points as for the Centigrade scale, 

 and making 100 of the new degrees cover 

 that range, it was found that the degrees 

 not only within that range, but as far be- 

 yond as experimental data supplied the 

 means of comparison, differed by only 

 minute quantities from those of Regnault's 

 air thermometer. The zero of the new 

 scale had to be determined by the consider- 

 ation that when the refrigerator was at the 

 zero of temperature the perfect engine 

 should give an amount of work equal to 

 the full mechanical equivalent of the heat 

 taken up. This led to a zero of 273 degrees 

 below the temperature of freezing water, 

 substantially the same as that deduced 

 from a study of the gaseous state. It was 



a great advance to demonstrate by the ap- 

 plication of the laws of thennodynamics 

 not only that the zero of temperature is a 

 reality, but that it must be located at 273 

 degrees below the freezing-point of water. 

 As no one has attempted to impugn the 

 solid foundation of theory and experiment 

 on which Lork Kelvin based his thermo- 

 dynamic scale, the existence of a definite 

 zero of temperature must be acknowledged 

 as a fundamental scientific fact. 



James Dewab. 



(To he concluded.) 



SCIENTIFIC BOOKS. 

 Essays in Historical Chemistry. By T. E. 



Thorpe, LL.D., F.R.S., Principal of the 



Government Laboratory, London. London 



and New York, Macmillan Co. 1903. 8vo. 



Pp. 582. 



This book, as explained in the preface, con- 

 sists mainly of lectures and addresses given 

 at various times to audiences of very different 

 type during the last twenty-five years. Al- 

 though the author says his book has no pre- 

 tensions to be considered a history of chemis- 

 try, even of the time to which the narratives 

 relate, it is in reality a most interesting and 

 charmingly written account of chemical dis- 

 covery and of the development of chemical 

 theory of the past century as connected with 

 the lives of the great men who have made the 

 science of chemistry what it is to-day. 



It is true that none of these essays deals 

 directly with Black, Dalton, Berzelius or Lie- 

 big, yet there is so much incidental mention 

 of the work of these investigators that their 

 places in the growing science are amply indi- 

 cated. 



Boyle, Priestley, Cavendish, Watt, Faraday 

 and Graham are the English subjects of these 

 addresses, and from the Continent we have 

 Scheele, Lavoisier, Wohler, Dumas, Kopp, 

 Victor Meyer, Mendeleeff and Cannizzaro, and 

 the latter group are as sympathetically treated 

 as the former. 



The author has the happy gift of making 

 the subjects of his study stand out vividly 

 as individuals, and we follow their careers, 



