292 Opacity and Green Colour of the Sea. [Book III. 



matter which the rays arrive at in the internal parts of 

 the water. 



The opacity of the fea, caufed by the numerous re- 

 flections from its internal parts, is Ib confiderable, that: 

 it is not near fo transparent as other water ; the reflec- 

 tive particles, therefore, which are difperfed through 

 the mafs of fea water, have confequently a greater re- 

 flective power than thofe which are difperfed through 

 the atmofphere. Inftead, therefore, of reflecting a de- 

 licate blue, fuch as that of the fky, the fea water, by 

 acting upon a greater portion of the more refrangible 

 rays, exhibits a green colour, which we know to be a 

 middle colour produced by the mixture of blue rays 

 with fome of the lefs refrangible, as the yellow or 

 orange. 



With refpect to the phenomena remarked by Dr. 

 Halley, it is eafy to conceive that the light, when (trip- 

 ped of all the more refrangible rays, fliould produce a 

 rofe colony fuch as that he obferved on the upper part 

 of his hand ; on the contrary, that which illuminated 

 the lower part of his hand confifted partly of rays re- 

 flected from the ground, and partly of thofe which 

 were reflected from the internal parts of the fea water, 

 which, we have feen, are chiefly blue and violet ; and 

 the mixture of thefe produced the greenim tinge which 

 the Doctor remarked *, and which common experience 

 mews is the predominant colour of the ocean. 



* Delaval on the caufts of colours in opake bodies, vol. ii 

 Manch. Mem. 



