28o GREAT MEN OF SCIENCE 



effected by Mayer, and quantitatively, by his calculation of 

 the mechanical equivalent of heat. All this was over- 

 looked by those who afterwards further developed Mayer's 

 ideas, and by those critics who did not give Mayer his due. 

 As often happens when an entrance door has been opened, 

 entry then appears as something quite natural, as though the 

 door had never been closed, and as though its discovery and 

 opening did not form the main achievement, after which all 

 further steps become almost a pastime. 



Why was it reserved for Mayer to find the entry, to recog- 

 nise and to open it, and even for himself to use it to survey 

 fairly thoroughly the new territory ? Why should he alone 

 (and, though in a hidden and unpublished form, Carnot, who 

 died young) have been chosen for this task, so that all others 

 could only follow, although they may have had similar 

 ideas, but had not brought them to this degree of perfection ? 

 Without any doubt, it must have been the peculiar nature of 

 Mayer's mind which enabled him to effect this, and it must 

 have been a very rare type of mind; for the ideas on which 

 the whole thing depended had been in the air, so to speak, 

 since Rumford's time, that is to say more than forty years, 

 inasmuch as the fact upon which they mainly depended had 

 been known for that length of time.^ 



Mayer's peculiar cast of mind had remained uninjured 

 by his previous training; for this training had never included 

 a school or university course in physics or mathematics, so 

 that his original freedom of mind to follow his own line of 

 thought had never been interfered with, and books had not 



1 The electrical phenomena, which had been the most recent dis- 

 coveiies, did not give any further impulse in this direction; on the con- 

 trary, when not considered very thoroughly, they appeared rather to 

 suggest again the possibility of a perpetual motion, as in the form of an 

 electromagnetic motor diiven by Voltaic elements. Even in the year 

 1 84 1, the Swiss government had offered a large prize for an electric loco- 

 motive which would be cheap to run (it was even thought that the chemi- 

 cal transformations in the cells might provide valuable by-products). 

 This offer was withdrawn in 1844. See Encyclopaedia Britannica, Art. 

 'Perpetual Motion ' 14th Ed., vol. 17, p. 540. 



