276 Mr. R. Hunt on the Changes which Bodies 
were subjected to mercurial vapour. On the iodized plate 
the deposit of vapour was uniform, although slight; but on 
the superposed plate of silver a strong and beautiful image of 
the string on the under plate became visible. I found that 
neither of the two iodized plates had lost their sensitiveness 
by the operations to which they had been subjected in the 
dark. 
Hoping to detect some evidence of the process by which 
these singular results were produced, I instituted a series of 
experiments, of which the following are some of the most in- 
teresting results. 
A. A silver plate was iodized, a piece of card was placed 
upon it, and a well-polished mercurial plate (amalgamated 
copper) was suspended ith of an inch above it, and left in this 
state fora night. ‘The space on the silver plate corresponding 
with the mercurial plate, except under the card, was nearly 
freed of its iodine, which had evidently combined with the 
mercury on the upper plate. On exposing the mercurial 
plate to the vapour of mercury the image of the card was ren- 
dered visible, the vapour covering every part of the plate ex- 
cept that opposite the card. The silver plate received the 
vapour only on those parts which were not influenced by the 
mercurial plate. The upper plate was suspended by strings; 
these were faithfully imaged on both plates; by a thick line 
of mercurial vapour on the under plate, by the absence of it 
in the upper one. 
B. An iodized silvered plate was exposed to light until 
brown, and a mercurial plate suspended above it for twelve 
hours. The browned silver plate was whitened, and all the 
irregularities of the mercurial plate strikingly marked on it: 
the mercurial plate was slightly tarnished. On rubbing the 
silvered plate it was found that the silver was removed most 
readily over the whitened portion, but had lost none of its ad- 
hesion in other parts. 
C. Over an iodized silver plate plates of gold, platina, 
silver, brass, copper, copper amalgamated, and zinc were 
placed at the distance of tth of aninch. After three hours the 
amalgamated plate had made a decided visible impression on 
the silver one. On exposure to vapour, the mercury lodged 
on every part of the plate but that affected by the mercurial 
plate; some irregularities were observed, but none which 
could be decidedly traced to the other metals in juxtaposi- 
tion. I have some evidence that different metals near each 
other seriously interfere with each other’s influence. 
D. A mercurial plate was iodized, and another mercurial 
plate placed 4th of an inch above it. The upper plate became 
