Mr. Hinds on Climate^ ^c. — Light, 469 



forations in the dead valves of Cyprina Islandica and Pecten Islandi- 

 cus ; not uncommon. 



The zoophytes enumerated in the preceding catalogue were 

 either collected during a three days' examination of the detri- 

 tus thrown upon the beach at Don-Mouth after a storm in 

 October 1841^ or are the result of a diligent and almost daily 

 search during the first fortnight of February 1 842, among the 

 objects brought up from deep water by the lines of the Foot- 

 dee fishermen. To the sixty-four species enumerated above, 

 in all probability many more remain to be added, but, being 

 about to leave the neighbourhood of the Aberdeeenshire coast, 

 I must leave this pleasing task to future observers. 



Old Aberdeen, February 23, 1842. ^ 



LT. — The Physical Agents of Temperature, Humidity, Light, 

 and Soil, considered as developing Climate, and in connexion 

 with Geographic Botany. By Richard Brinsley Hinds, 

 Esq., Surgeon R.N. 



[Conthiued from p. 333.] 



III. Light. 



Light and heat are so intimately connected and so generally 

 accompany each other, that the laws of one are very nearly 

 those of the other. Both are of the utmost importance to ve- 

 getation, and it is not easy to allow a superior influence to 

 either, each in its turn, when coming under consideration, ap- 

 pearing to claim priority. Light is pre-eminently active in 

 the functions depending on the alternation of day and night, 

 in fixing the more solid constituents, and in bestowing rich- 

 ness of colour and secretion. 



Sir Isaac Newton, by means of the prism, separated solar 

 light into seven distinct rays, which from their properties he 

 called colorific. These were red, orange, yellow, green, blue, 

 indigo and violet ; and they were found to possess different de- 

 grees of refrangibility, it being greatest in the violet and least 

 in the red. A method was now developed for explaining the 

 numerous shades of colour in substances ; black was ascribed 

 to the absorption of all the rays, white to their reflection, and 

 every variety of tint or colour was due to the partial reflection 

 of certain rays and the absorption of all the others. More 

 recently it has been proved by Sir David Brewster that these 

 seven colours are resolvable into three primary rays, red, yel- 

 low and blue ; orange being formed by a mixture of red and 

 yellow, green by yellow and blue, indigo and violet by red and 



