208 FRAGMENTS OF SCIENCE. 



and vibrations, and waves, which eye has never seen nor 

 ear heard, and which can only be discerned by the exercise 

 of imagination. This, in fact, is the faculty which enables 

 us to transcend the boundaries of sense, and connect the 

 phenomena of our visible world with those of an invisible 

 one. Without imagination we never could have risen to 

 the conceptions which have occupied us here to-day ; and 

 in proportion to your power of exercising this faculty aright, 

 and of associating definite mental images with the terms 

 employed, will be the pleasure and the profit which you 

 will derive from this lecture. The outward facts of Nature 

 are insufficient to satisfy the mind. We cannot be content 

 with knowing that the light and heat of the sun illuminate 

 and warm the world. We are led irresistibly to inquire 

 what is light, and what is heat ? and this question leads us 

 at once out of the region of sense into that of imagination. 

 Thus pondering, and questioning, and striving to sup- 

 plement that which is felt and seen, but which is incom- 

 plete, by something unfelt and unseen which is necessary 

 to its completeness, men of genius have in part discerned, 

 not only the nature of light and heat, but also, through 

 them, the general relationship of natural phenomena. The 

 working power of Nature is the power of actual or poten- 

 tial motion, of which all its phenomena are but special 

 forms. This motion manifests itself in tangible and in in- 

 tangible matter, being incessantly transferred from the one 

 to the other, and incessantly transformed by the change. 

 It is as real in the waves of the ether as in the waves of 

 the sea ; the latter, derived as they are from winds, which 

 in their turn are derived from the sun, being nothing more 

 than the heaped-up motion of the former. It is the calo- 

 rific waves emitted by the sun which heat our air, produce 

 our winds, and hence agitate our ocean. And whether they 

 break in foam upon the shore, or rub silently against the 

 ocean's bed, or subside by the mutual friction of their own 



