GALILEO AND HIS JUDGES. 137 



that either the Sun goes round the Earth in the course 

 of a year, or else that the Earth goes round the Sun. 

 The question is how these facts are to be accounted for. 



The first of the two errors I have just mentioned 

 is that which supposes the Copernican theory to 

 have been directly and conclusively proved. This I 

 imagine to be very common, and to arise from the 

 elementary books learnt by schoolboys, which state 

 (naturally enough) the modern theory of astronomy 

 without the reasons that support it. 



We need not dwell long on this point. Persons 

 who have got this erroneous impression misunder- 

 stand the nature of the evidence. Some things in 

 astronomy can be positively proved from observation, 

 as, for instance, the existence of sun-spots. Many 

 things in mechanics, chemistry, optics, and other 

 branches of physical study can be demonstrated by 

 experiment. The motion of the Earth round the Sun 

 cannot, however, be so treated. It is inferred, and 

 very rightly so, from the fact that it explains com- 

 pletely and easily all the observed phenomena, while, 

 on the other hand, there are certain things which, as 

 far as our present ^knowledge goes, cannot be ex- 

 plained in any other way ; and the same argument 

 applies to the rotation of the Earth on its axis. But 

 though all this is perfectly clear so far, who can 

 possibly say that as science progresses some explana- 

 tion may not be hereafter found consistent with the 

 antagonistic theory consistent, let us say, with the 

 system of Tycho Brahe, or some modification of it ? 



