THE ASTRONOMICAL VIEW OF NATURE. 309 

 the mind of Whewell when, after writing his his- e. 



Whewell's 



torical work, he attempted in the philosophical sequel ^^p 1 ^' 

 to abstract the general ideas which have led scientific os P h y-' 

 research; but it is instructive for our present purpose 

 to note how, writing about the middle of the century, 

 he hardly brought out any of those principles which 

 in the course of its second half have turned out to 

 be fruitful, and have almost become watchwords of 

 popular science. In the year 1857, the date of the 

 publication of the latest editions of Whewell's works, 

 nothing was popularly known of energy, its conserva- 

 tion and dissipation, nothing of the variation of species, 

 and the evolution of organic forms, nothing of the 

 mechanical theory of heat or of that of gases of 

 absolute measurements and absolute temperature; even 

 the cellular theory seems to have been popular only in 

 Germany. And yet all the problems denoted by these 

 now popular terms were then occupying, or had for many 

 years occupied, the leading thinkers of that period. But 

 we find no mention of them in Whewell's works. 1 So 



1 The dates of the birth of these 

 leading ideas of the second half of 

 our century are approximately as 

 follows : 



Absolute measurements were 

 started by Gauss about 1830, and 

 the scheme published in 1833 in 

 his memoir, ' Intensitas vis magne- 

 ticse terrestris ad mensuram absolu- 

 tam revocata. ' They were extended 

 to electrical phenomena by Weber in 

 his 'Electrodynamische Maasbestim- 

 mungen,' 1846. The absolute scale 

 of temperature was introduced by 

 William Thomson in 1848. 



The cellular theory was pro- 

 pounded by Schleiden in 1838, and 



extended to animal structures by 

 Schwann in 1839 ; the term "pro- 

 toplasm " was introduced by Mohl 

 in 1846. 



The mechanical theory of heat 

 dates from Mayer's and Joule's de- 

 terminations of the equivalent of 

 heat in 1842 and 1843. 



The doctrine of the conservation 

 of energy dates from Helmholtz's 

 memoir, ' Ueber die Erhaltung der 

 Kraft,' in 1847 ; that of dissipation 

 of energy from William Thomson's 

 paper " On a Universal Tendency 

 in Nature to the Dissipation of Me- 

 chanical Energy." 1852 ; it was 

 prepared by Watt's and Poncelet's 



