DESCRIPTIO GLOBI INTELLECTUALIS. 271 



an accurate knowledge of the phenomena, and then 

 :i to search out their real causes. Orbs, eccentrics, 

 and epicycles must not stand between the astronomer 

 and the farts with which he has to deal. In this lan- 

 guage, which had been held by others, there is some- 

 thing not wholly untrue ; yet the counsel which it 

 contains would, if it could have been followed, have 

 put an end to the progress of astronomical science. Let 

 us obtain an accurate knowledge of the phenomena 

 this no doubt is necessary, but then how is it to be 

 done ? To say that instead of trying to resolve the 

 motion of the planets into a combination of elementary 

 circular motions, we ought to be content to save the 

 appearances by means of spirals, is to no purpose unless 

 tiv prepared to give an accurate definition of the 

 kind of spiral we mean. Failing this, a statement that 

 the apparent path of a planet is a spiral or irregular 

 line along which it moves with varying velocity, is 

 much too vague to be of any scientific value whatever; 

 and if we seek to give precision to this statement, we 

 find ourselves led back again into the region of mathe- 

 matical conceptions, or, if the phrase be preferred, of 

 mathematical hypotheses. The distinction between 

 what is real and what is only apparent lies at the root 

 of all astronomy ; and it is in vain to seek for a physical 

 cause of that which has only a phenomenal existence, 

 as for instance of the stations and regressions of the 

 planets. Thus in two points of view, astronomy must 

 of iierL'-.-ity employ mathematical hypotheses, firstly in 

 order to the distinct conception of the phenomena, and 

 secondly in order to be able to state the problems which 

 a hi_ -nee is afterwards to solve. If the hypoth- 



cmployed are inappropriate, as in the systems of 



