CONDITIONS OF ASTRONOMIC PROGRESS. 143 



nsed to distinguish the heavenly bodies that are of like na- 

 ture with the sun from those which are not. It was thus 

 when, as recently, an electro-telegraphic instrument was in- 

 vented for the more accurate registration of meridional 

 transits. It was thus when the difference in the rates of a 

 clock at the equator, and nearer the poles, gave data for 

 calculating the oblateness of the earth, and accounting for 

 the precession of the equinoxes. It was thus — but it is 

 needless to continue. 



Here, within our own limited knowledge of its history, we 

 have named ten additional cases in which the single science 

 of astronomy has owed its advance to sciences coming after 

 it in M. Comte's series. Not only its secondary steps, but 

 its greatest revolutions have been thus determined. Kep- 

 ler could not have discovered his celebrated laws had it not 

 been for Tycho Brahe's accurate observations ; and it was 

 only after some progress in physical and chemical science 

 that the improved instruments with which those observa- 

 tions were made, became possible. The heliocentric theory 

 of the solar system had to wait until the invention of the 

 telescope before it could be finally established. Nay, even 

 the grand discovery of ail — the law of gravitation — depend- 

 ed for its proof upon an operation of physical science, the 

 measurement of a degree on the Earth's surface. So complete- 

 ly indeed did it thus depend, that Newton had actually 

 abandoned his hypothesis because the length of a degree, 

 as then stated, brought out wrong results ; and it was only 

 after Picart's more exact measurement was published, that 

 he returned to his calculations and proved his great gener- 

 aUzation. Now this constant intercommunion, which, for 

 brevity's sake, we have illustrated in the case of one science 

 only, has been taking place with all the sciences. Through- 

 out the whole course of their evolution there has been a 

 continuous consensus of the sciences — a consensus exhibit- 

 ing a general correspondence with the consensus of facul- 



