274 Mr. R. Hunt on the Changes which Bodies 
were active in producing the effects described by Dr. Draper, 
Moser and myself. I however obtained the most decided 
evidence that no effect was produced by an exposure of two 
hours to the prismatic spectrum by the most refrangible rays ; 
but it frequently happened in these trials, that much mer- 
curial vapour was deposited about that part of the metal on 
which the rays of least refrangibility fell: These experiments 
were, however, by no means satisfactory; but I hope, with 
the increase of light and the required instruments, to exa- 
mine the question minutely this summer. 
The coloured media used by me were,—1, red ; 2, yellow; 
3, green; 4, blue: these insulated respectively the following 
rays :— 
‘ Red, orange, yellow, and some of the blue, 
2. Orange, yellow, green, with a faint trace of the blue, 
and a small portion of the red. 
3. Orange, yellow, green, and blue. 
4. Green, blue, indigo, and violet. 
In addition to these fluids, water (5), and water blackened 
with ink (6), were also used. 
A very highly polished plate of copper with the above 
media in flint-glass flat bottles laid upon it, was exposed to 
bright sunshine for one hour. It was then placed in a dark 
box, and subjected to the vapour of mercury. The largest 
deposit of mercury was found to mark the space occupied by 
the red fluid (1); the next in order was that influenced by 
the blue (4), and then the others as follows: green (3), yel- 
low (2), white (5), and black (6). There was less mercury 
deposited where the last four bottles of fluids had lain than 
on the uncovered portions of the plate. Precisely the same 
arrangement as the above was kept in the dark for five hours, 
and the plate then exposed to mercurial vapour, which at- 
tacked it in the same manner as when subjected to strong 
sunshine, except that no mercury was deposited on the un- 
covered parts of it. 
Another copper plate was placed one-eighth of an inch 
above the same bottles of fluids in the dark, and allowed to 
remain in that position for five hours. On exposure to the 
vapour of mercury, it was found that the only impressions 
were made on those parts opposite the red fluid (1), the 
blue (4), and the green (3), the largest deposits correspond- 
ing with the red fluid; but that portion opposed to the green 
fluid (3) exhibiting the slightest possible traces of action. 
I cannot explain any of the peculiarities which I have now 
described ; they belong to a class of phenomena of the most 
mysterious kind, and the elucidation will only be effected by 
