HOW THE SCIENCES AID EACH OTIIEE. 183 



impression that, with but trifling exceptions, the sciences 

 aid each other only in the order of their alleged succession. 

 The fact is, however, that the division of labour in science, 

 like the division of labour in society, and like the &quot; physio 

 logical division of labour &quot; in individual organisms, has been 

 not only a specialization of functions, but a continuous help 

 ing of each division by all the others, and of all by each. 

 Every particular class of inquirers has, as it were, secreted 

 its own pai ticular order of truths from the general mass of 

 material which observation accumulates ; and all other 

 classes of inquirers have made use of these truths as fast 

 as they were elaborated, with the effect of enabling them 

 the better to elaborate each its own order of truths. 



It was thus in sundry of the cases we have quoted as at 

 variance with M. Comte s doctrine. It was thus with the 

 application of Huyghens s optical discovery to astronomical 

 observation by Galileo. It was thus with the application 

 of the isochronism of the pendulum to the making of in 

 struments for measuring intervals, astronomical and other. 

 It was thus when the discovery that the refraction and dis 

 persion of light did not follow the same law of variation, 

 affected both astronomy and physiology by giving us achro 

 matic telescopes and microscopes. It was thus when Brad- 

 ley s discovery of the aberration of light enabled him to 

 make the first step towards ascertaining the motions of the 

 stars. It was thus when Cavendish s torsion-balance ex 

 periment determined the specific gravity of the earth, and 

 so gave a datum for calculating the specific gravities of the 

 sun and planets. It was thus when tables of atmospheric 

 refraction enabled observers to write down the real places 

 of the heavenly bodies instead of their apparent places. It 

 was thus when the discovery of the different expansibilities 

 of metals by heat, gave us the means of correcting our 

 chronometrical measurements of astronomical periods. It 

 was thus when the lines of the prismatic spectrum were 



