174 FRAGMENTS OF SCIENCE. 



from some places and concentrated upon others, the 

 water flashing with metallic lustre. The screw-blades 

 in this case played the part of the dinner-plate in the 

 former case, and there were other instances of a similar 

 kind. The white bellies of porpoises showed the green 

 hue, varying in intensity 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 reached the eye, a beauti- 

 ful green cap being thus placed upon the wave, even 

 in indigo water. 



But how is this colour 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 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 dif- 

 fused through the clear sea-water, it would also send 

 green light to the eye. In fact, the suspended particles 

 which the home examination reveals, act in all essen- 

 tial 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 con- 

 nected 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. 



