familiar to us, that we contemplate them without being 

 reminded of their origin ; until they become, as it were, 

 a part of ourselves. The feeling of gratitude for the 

 source of any individual truth, must be swallowed up in 

 the higher and more general feeling of veneration for the 

 perception of that harmony and unity which fills the 

 soul with admiration. We are thus prone to overlook 

 the influence which science silently, and almost insen- 

 sibly, exercises on the development of the powers of 

 the imagination. No mind is exempt from the influence 

 of the great physical discoveries of the last three cen- 

 turies ; no one perceives it at any particular -moment, 

 though all are at every moment subject to it. To con- 

 template often the great truths brought under the com- 

 prehension of man, is thus almost to dwell in a sort of 

 social communion with the everlasting source of truth. 

 The influence of the general diffusion of knowledge 

 may — to borrow an illustration from Seneca — in this 

 respect, be compared to that of light, which it is impos- 

 sible to approach, without deriving from it some faint 

 coloring, even though we should not sit in the very 

 sunshine ; or to that of precious odors, amid which we 

 cannot long remain, without bearing away with us some 

 portion of the fragrance. (Seneca, Ep. 108.) 



The physical philosopher who measures with admirable 

 sagacity the waves of light of unequal length, which, by 

 concurrence or interference, mutually strengthen or de- 

 stroy each other ; or who, by the comparison of a long 

 series of observations, is able to trace a periodicity in the 

 secular variation of the magnetic needle, which corres- 

 ponds with the variation in the spots on the sun ; or who, 

 by means of a revolving mirror, proves that the velocity 



