212 HISTORY OF PHYSICAL ASTRONOMY. 



and thus the prevalence of the Cartesian system 

 did not seriously impede the progress of sound 

 knowledge. In some cases, no doubt, it made men 

 unwilling to receive the truth, as in the instance 

 of the deviation of the comets from the zodiacal 

 motion; and again, when Romer discovered that 

 light was not instantaneously propagated. But it 

 encouraged observation and calculation, and thus 

 forwarded the verification and extension of the 

 Newtonian system ; of which process we must now 

 consider some of the incidents 



