4; 8 Notices 7-especiing New Books. 



the primitive form of the crystal be neither a cube nor a regular oc- 

 tahedron, it is split into two distinct rays, one of which is refracted in 

 the ordinary way, while the other suffers an extraordinary refraction. 

 Hence when an object is viewed through such a crystal it appears 

 double, and therefore such bodies are said to refract doubly. — Dr. 

 Thomson's System, vol. i. p. 15. 



Is light a simple body, that is, are the rays of light indivisible ? 

 No : light is separable by a prism into seven primary rays or co- 

 lours, as well as into others which appear to be distinguished by cer- 

 tain chemical powers. For instance, if a ray of light in passing 

 through a small hole, with a prism near it, be made to fall on a sheet 

 of white paper, a spectrum is produced, composed of seven distinct 

 colours, viz. red, orange, yellow, green, blue, indigo, violet. — 

 The first three lines from Dr. Pariss Medical Chemistry, p. 225 j the 

 lines in italics slightly altered from Dr. Fyfe's Manual, and the re- 

 mainder from the same work, p. 95. 



7s there any difference in the power of illumination in these rays ? 

 They have very different illuminating powers. Thus, if a small ob- 

 ject is placed at either end of the spectrum, it is seen indistinctly, but 

 if brought towards the centre, it becomes much more distinct, the 

 greatest illuminating power being between the bright yellow and the 

 pale green. — Dr. Fyfe"s Manual, p. 96. 



Tf'hat was Sir Isaac Newton's opinion with respect to the cause of 

 the different colours of bodies ? 



That it is owing to their power of absorbing all the primitive colours, 

 except the peculiar one which they reflect, and of which colour they 

 therefore appear to our eye. 



This is the only complete answer which we have hitherto met with, 

 the author of which does not occur to us. 



Is not solar light capable of producing great chemical changes? 

 Yes. A familiar instance of this is the blackening of indelible or 

 marking ink, the traces of which are at first invisible, but soon be- 

 come black on exposure to sunshine, or even the day light, from the 

 decomposition of the salt of silver which it contains. — Fyfe's Manual, 

 pp. 97 and 98. 



Then the solar light is composed of three distinct rays: have the 

 goodness to recapitulate them ? 



They are, 1st, the luminous rays affording light ; 2nd, the calo- 

 rific causing heat ; and 3rd, the chemically acting ray. — Slightly al- 

 tered from Fyfe's Manual, p. 98. 



Are you aware of any marked ejects which light has on the vegetable 

 and animal creation P 



I am sensible that the agency of light exerts a remarkable influence 

 over both the vigour and colour of vegetables and animals. Plants, for 

 instance, may be made to vegetate tolerably well in the dark, but 

 then their colour is always white, they have scarcely any taste, and 

 contain but a very small proportion of combustible matter. In a very 

 short time, however, after their exposure to light, their colour be- 

 comes green, their taste is rendered much more intense, and the 

 quantity of combustible matter is considerably augmented. The co- 

 lour 



