154 GALILEO AND HIS JUDGES. 



Newton, extends not only through our own solar 

 system, but over the whole material universe. 



And there is one remarkable property of this myste- 

 rious agency which we term gravitation, and that is 

 its instantaneous action even at the greatest distances. 

 Light travels with an enormous and yet a finite velo- 

 city, so that it takes a few years to arrive at the Earth 

 from even the nearest stars. The force of gravity 

 knows no such limit, nor is its action retarded by even 

 the minutest fraction of time. 



Nor, again, is it impeded, as in the case of light, 

 by any screen or obstacle of whatever nature. Further- 

 more, it does not lose anything of its intensity, as 

 light does, by being diffused over a larger surface ; it 

 varies as the mass of the bodies concerned, but not in 

 the least according to the extent of their surfaces. 

 Given the same distance, no diffusion weakens its 

 force. 



Great as was the evidence adduced by Newton for 

 the truth of his theory, there were some real difficul- 

 ties in the way of its reception. I need not allude to 

 these in detail ; they are explained in treatises on 

 physical astronomy for the benefit of those who are 

 interested in the subject. Briefly, I may say that 

 subsequent research and careful calculations have 

 removed the difficulties, and thereby confirmed the 

 already existing evidence. 



Then, as regards terrestrial gravity, experiments 

 have been made notably at the mountain Schehallion, 



