210 
self from the implications contained in his letter. Had my 
time permitted I should have replied to this charge at an 
earlier date, but professional engagements have rendered this 
delay unavoidable. 
In the communication read before the Chemical Society 
on February 1, 1842, and afterwards inserted in your Journal 
of September of the same year, I do not lay any claim to the 
discovery of many of the phenomena therein detailed; nay 
more, it is distinctly stated (p. 193), ** The resumption of the 
scarlet colour (in the sublimed yellow crystals of the biniodide) 
has been attributed to an alteration in the molecular arrange- 
ment of the crystals, and it was with the view of clearly ascer- 
taining this point that the following microscopic investigations 
were undertaken.” Iam at a loss to imagine how this can be con- 
strued into any wish on my part to deprive Mr. Talbot of what 
he claims as his discovery. But we must proceed to examine 
this matter with more care. In 1830the alleged discovery of Mr. 
Talbot of 1836 was shown me by Mr. J.T. Cooper, with whom 
I was then assistant, and in the same year the phenomena 
claimed were exhibited as class-room illustrations; however, 
we must go even further back to the original paper on the 
subject by M. A. Hayes, and which was published in the 
American Journal of Science and Arts for 1829, vol. xvi. 
p- 174. This paper was republished in the Quarterly Jour- 
nal of Science of the Royal Institution for 1830, p. 208; and 
it was noticed in the Paris edition of Berzelius’s Trazté de 
Chémie of 1830. Irrespective of these facts, the observations 
made by M. A. Hayes are so exactly those claimed by Mr. 
Talbot in his November paper, that I feel bound to place them 
in juxtaposition. 
Mr. Fox Tazzort, 1836. 
“In that memoir (Phil. Mag., 
Mr. Warington on the Biniodide of Mercury. 
M. A. Haves, 1829. 
‘Ifthe precipitate, obtained as 
1836, S. 3. vol. ix. p. 1.) I have 
shown,— 
“1st. That when iodide of 
mercury is sublimed between two 
plates of glass nearly in contact 
with each other, it cools in the 
form of thin rhombic plates of a 
pale yellow colour. 
“©Ond. These often retain their 
colour when cold, if left undis- 
turbed. 
«3rd. But if such a crystal is 
disturbed, as for example, by 
touching it with a needle at any 
above, by the addition of iodide 
of iron in solution to one of bi- 
chloride of mercury, be heated in 
a small subliming apparatus, or in 
a glass tube, it melts and sublimes 
copiously, and the vapour is con- 
densed in large transparent rhom- 
bic plates, of a fine sulphur yel- 
low colour. 
*«« These crystals are permanent 
in the air and unaltered by the 
direct solar rays ; but the slight- 
est friction or the contact of a fine 
point, is sufficient to alter their 
interior arrangement. The point 
