132 FRAGMENTS OF SCIENCE. 



whose love of causal unity tempts them perpetually 

 to break through the limitations of the senses, and to 

 seek beyond them the roots and reasons of the pheno- 

 mena which the observer and experimenter record. 

 To such spirits adventurous and firm we are indebted 

 for our deeper knowledge of the methods by which the 

 physical universe is ordered and ruled. 



In his efforts to cross the common bourne of the 

 known and the unknown, the effective force of the man 

 of science must depend, to a great extent, upon his 

 acquired knowledge. But knowledge alone will not 

 do ; a stored memory will not suffice ; inspiration must 

 lend its aid. Scientific inspiration, however, is usually, 

 if not always, the fruit of long reflection of patiently 

 'intending the mind/ as Newton phrased it; and as 

 Copernicus, Newton, and Darwin practised it; until 

 outer darkness yields a glimmer, which in due time 

 opens out into perfect intellectual day. From some of 

 his expressions it might be inferred that Newton scorned 

 hypotheses ; but he allowed them, nevertheless, an open 

 avenue to his own mind. He propounded the famous 

 corpuscular theory of light, illustrating it and defending 

 it with a skill, power, and fascination which sub- 

 sequently won for it ardent supporters among the best 

 intellects of the world. This theory, moreover, was 

 weighted with a supplementary hypothesis, which as- 

 cribed to the luminiferous molecules ' fits of easy 

 reflection and transmission,' in virtue of which they were 

 sometimes repelled from the surfaces of bodies and 

 sometimes permitted to pass through. Newton may 

 have scorned the levity with which hypotheses are 

 sometimes framed ; but he lived in an atmosphere of 

 theory, which he, like all profound scientific thinkers, 

 found to be the very breath of his intellectual life. 



The theorist takes his conceptions from the world 



