186 FBAGMENTS OF SCIENCE 



pended 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 microscopic 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 condition diffused through the clear sea- 

 water, it would also send green light to the eye. In fact, 

 the suspended particles which the home examination re- 

 veals act in all essential particulars like the plate, or like 

 the screw-blades, or like tho foam, or like the bellies of 

 the porpoises. Thus I think the greenness of tne 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 not 

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

 aspects of nature and the kindliness of men. 



