250 BRAMBLES AND BAY LEAVES. 
slightly, and a thermometer placed at the red end of the 
spectrum shows a higher temperature than one placed 
at the blue end, which blue end the photographer 
requires for his operations, in converting a shadow into 
a picture—as fixed as if painted in enduring pigments. 
If the heating power of the blue ray be counted one, 
that of the green will be two , and that of the red more 
than three and a half, and that of the colourless part just 
beyond the red about four and a half. The ripe peach, 
glowing with a vermilion blush, shows a response to the 
red rays by which it elaborated its sweet juices; the 
ripe apple, burning with red on the side next the sun, 
tells me of oxygen, the sourer, incorporated into an acid, 
by that very pencil of red light which forms the boun¬ 
dary at one side of the rainbow. The fading of my red 
window-curtains tells me of the energy of the blue rays 
in de-oxydising; for the pigment the manufacturer used 
was an oxide, and the blue rays mixed with the ordinary 
daylight, constantly operate in setting free the oxygen, 
and restoring the oxide to its metallic form. Three 
colours, three powers, and these variously proportioned 
in every climate of the world, so as to produce flowers 
of intensest hues, and fruits of delicious flavours, in the 
tropics, and in this country only during summer; pale- 
coloured flowers and less sugary fruits, in colder climates 
and at colder seasons in this country. The frame of 
nature seems now to be suspended on the rainbow— 
wonderful fabric, to be upheld by so fragile a thread! 
What is the story of Damocles to this enigma of the 
motherly Sphynx ? 
The grey of the evening thickens, the sun is nearly 
