132 FRAGMENTS OF SCIENCE. 



sity as the creatures swung to and fro between the surface 

 and the deeper water. Foam, at a certain depth below 

 the surface, was also green. In a rough sea the light 

 which penetrated the summit of a wave sometimes 

 readied the eye, a beautiful green cap being thus placed 

 upon the wave, even in indigo water. 



But how is this color to be connected with the suspended 

 particles? Thus. Take the dinner-plate which showed so 

 brilliant a green when thrown into indigo water. Suppose 

 it to diminish in size, until it reaches an almost micro- 

 scopic magnitude. It would still behave substantially as 

 the larger plate, sending to the eye its modicum of green 

 light. If the plate, instead of being a large coherent mass, 

 were ground to a powder sufficiently fine, and in this con- 

 dition diffused through the clear sea-water, it would also 

 send green light to the eye. In fact, the suspended par- 

 ticles which the home examination reveals, act in all 

 essential particulars like the plate, or like the screw-blades, 

 or like the foam, or like the bellies of the porpoises. Thus 

 I think the greenness of the sea is physically connected 

 with the matter which it holds in suspension. 



We reached Portsmouth on January 5', 1871. Then 

 ended a voyage which, though its main object was riot 

 realized, has left behind it pleasant memories, both of the 

 aspects of nature and the kindliness of men. 



CHAPTER VII. 



NIAGARA.* 



IT is one of the disadvantages of reading books about 

 natural scenery that they fill the mind with pictures, often 

 exaggerated, often distorted, often blurred, and, even 

 when well drawn, injurious to the freshness of first im- 

 pressions. Such has been the fate of most of us with re- 

 gard to the Falls of Niagara. There was little accuracy in 

 the estimates of the first observers of the cataract. Startled 

 by an exhibition of power so novel and so grand, emotion 



* A Discourse delivered at the Royal Institution of Great Britain, 

 April 4, 1873, 



