chemical Properties attributed to Light. 453 
The heat which existed at that distance from the flame, on 
the side of it, where this coloured stripe was produced, was suf- 
ficiently intense, as I found by experiment, to melt very fine 
silver wire, flatted, such as is used in making silver lace. 
The objects I had in view in the following experiments, are 
too evident to require any particular explanation. 
Experiment No. 5. Two like pieces of riband were wetted 
at the same time in the solution, and suspended, while wet, in 
two thin phials, A and B, of very transparent and colourless 
glass ; the mouths of the phials being left open. Both these 
phials were placed in a window which fronted the south ; that 
distinguished by the letter A being exposed naked to the direct 
rays of a bright sun ; while B was inclosed in a cylinder of paste- 
board, painted black within and without, and closed with a fit 
cover, and consequently remained in perfect darkness. 
In a very few minutes, the riband in the phial A began sen- 
sibly to change its colour, and to take a purple hue ; and, at 
the end of five hours, it had acquired a deep crimson tint 
throughout. 
The phial B was exposed in the window, in its dark cylin- 
drical cover, three days ; but there was not the smallest appear- 
ance of any change of colour in the silk. 
Experiment No. 6. Two small parcels of magnesia alba, in 
an impalpable powder, (about half as much in each as could be 
made to lie on a shilling,) were placed in heaps, in two China 
plates, A and B, and thoroughly moistened with the before- 
mentioned aqueous solution of the oxide of gold. Both » 
plates were placed in the same window; the moistened earth 
in the plate A being exposed naked to the sun’s rays ; while 
x 
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