28 FKAOMENTS OF SCIENCE. 



upon the moon; a body 240,000 miles, or sixty times 

 the earth's radius, from the earth's centre. He 

 virtually weighed the moon, and' found that weight to 

 be 3-gVot n f wna t it would be at the earth's surface. 

 This is exactly what his theory required. I will not 

 dwell here upon the pause of Newton after his first cal- 

 culations, or speak of his self-denial in withholding 

 them because they did not quite agree with the 

 observations then at his command. Newton's action in 

 this matter is the normal action of the scientific mind. 

 If it were otherwise if scientific men were not accus- 

 tomed to demand verification if they were satisfied 

 with the imperfect while the perfect is attainable, their 

 science, instead of being, as it is, a fortress of adamant, 

 would be a house of clay, ill-fitted to bear the buffetinga 

 of the theologic storms to which it is periodically 

 exposed. 



Thus we see that Newton, like Torricelli, first pon- 

 dered his facts, illuminated them with persistent 

 thought, and finally divined the character of the force 

 of gravitation. But, having thus travelled inward to 

 the principle, he reversed his steps, carried the principle 

 outwards, and justified it by demonstrating its fitness 

 to external nature. 



And here, in passing, I would notice a point which 

 is well worthy of attention. Kepler had deduced his 

 laws from observation. As far back as those observa- 

 tions extended, the planetary motions had obeyed these 

 laws ; and neither Kepler nor Newton entertained a 

 doubt as to their continuing to obey them. Year after 

 year, as the ages rolled, they believed that those laws 

 would continue to illustrate themselves in the heavens. 

 But this was not sufficient. The scientific mind can 

 find no repose in the mere registration of sequence in 

 nature. The further question intrudes itself with 



