NEWTON'S THEORY OF PLANETARY MOTIONS 69 



the query, Why may not the planetary orbits be other 

 than circular! These two ideas, epochal though they 

 proved, were by no means strokes of genius, but only the 

 prosaic promptings of common sense erupting through 

 the smothering strata of superstition, tradition, and 

 mathematical abstrusities that the wiseacres of earlier 

 centuries had heaped up. So far as the mathematical 

 proof was concerned, that was only a matter of rules and 

 industry, once given the clue. Clearly, the two most im- 

 portant lessons of astronomical history are, (1) that 

 vigilant skepticism is the price of progress, and (2) that 

 investigation should begin with the near and obvious. 



The next great name in the development of the 

 science is that of Rene Descartes (1596-1650), although 

 he is seldom thought of as an astronomer, but rather as a 

 philosopher and mathematician. I mention him here, 

 partly because it was his cult whose ascendancy over the 

 world of thought for almost a century after his death 

 was great enough to bar out of England's schools the 

 teachings of her own son, Sir Isaac Newton (1642-1727), 

 during the whole of that philosopher's long life, and 

 partly because he, Descartes, was the originator of the 

 Vortical theory of planetary motions ; a theory which, 

 though utterly impractical as he conceived it, we shall 

 nevertheless find to be true in principle when combined 

 with the workings of universal gravitation. 



It is with sincere regret that I must confess my ina- 

 bility to share the world's extravagant estimate of New- 

 ton as a pliilosophical astronomer. As a mathematician 

 he may possibly have been supreme ; but of this I am not 

 competent to judge. Was it not Huxley who first said 

 that you cannot take out of mathematics more than you 

 put in it meaning, that if you start figuring upon false 

 premises you cannot arrive at useful results? Because 

 a man is a mathematical genius, does not signify that he 

 is equally great, or even great at all, as a theorist or con- 

 structor. Ptolemy was a mathematician of the first 

 order, but his crystalline spheres and epicycles were, for 

 all that, fantastic unrealities. In our day the Nebular 

 Hypothesis of Laplace (perhaps a greater natural mathe- 



