are capable of undergoing in Darkness. 277 
covered with a bright yellow film; and on exposing them to 
mercurial vapour, marks became apparent which corresponded 
with those in the opposite plate. 
E. A silver plate was iodized and placed in the dark with 
an engraving, face down, upon it. An amalgamated copper 
plate was laid on this, and left for fifteen hours. ‘The mer- 
curial plate was reddened, and on exposure to the vapour of 
mercury, a very nice impression of the engraving was brought 
out, it having been effected through the thickness of the 
paper. On the silvered plate the space covered by the paper 
was well marked; but vaporization produced no trace of the 
engraving. ‘The space beyond the paper was rendered white. 
It was curious that both plates had several spots which cor- 
responded, particularly two, distinguished by a well-defined 
circle and a comet-like appendage, in length ten times the 
diameter of the circle. These spots could not be traced to 
anything visible in the print or either of the plates, and must, 
I think, be referred to some electrical influence. I find it in- 
deed commonly the case, that the plates, after being subjected 
to these kinds of experiments a few times, become mottled, 
or present on their polished faces all the appearances of a 
finely-grained wood, and in this state they are less susceptible 
of receiving any impression than when not so. 
F. A silver plate was iodized and placed upon an engraving 
Jaid on a brightly polished mercurial plate, and left in the 
dark for twenty-four hours. ‘The mercurial plate was turned 
brown, and the silver plate was left in the same state as if it 
had been exposed to sunshine, being brown and black. Neither 
of these plates gave a copy of the picture. 
G. A mercurial plate was iodized, and above it was placed 
a plate of polished iron, a disc of paper being first laid on the 
mercurial plate, and they were left in this state for some hours. 
On exposing the iron plate to mercurial vapour, it was abun- 
dantly lodged over that space opposite the paper disc, but not 
at all on the other parts. The mercurial plate was attacked 
by vapour over every part but that which the paper disc pro- 
tected. 
Lead and zinc plates were used instead of the iron one 
with nearly similar results. 
H. A Daguerreotype view was taken, and without removing 
the iodine a mercurial plate was placed a little above it, and 
left for ten hours. When removed, well-defined traces of 
the Daguerreotype picture were evident on the mercurial 
plate, which leads me to hope that by careful manipulation 
we may succeed in multiplying these beautiful productions by 
an easy method. 
