298 New Book: Daniell’s Chemical Philosophy. 
of scientific justice, such as inevitably must frequently be made 
in these days of unexampled activity in experimental research ; 
for no one can possibly be expected to read and remember 
all that is published in the journals of science at home and 
abroad. Mistakes are therefore continually occurring. Dis- 
coveries already made are again published as new. When 
this happens, no other course is open than to point out the 
error, and to correct it in as few words as possible. This is 
what I intended to do, and it was my only object in address- 
ing to you my short letter on the subject. ‘The credit that 
may be due to any scientific discovery, whatever it may be, 
ought assuredly to be awarded to the first discoverer, and 
that with all the care and correctness that is possible; and I 
am quite ready and willing to see this principle fairly and im- 
partially applied in all cases—more particularly in the pre- 
sent one. 
Mr. W. has satisfactorily shown that the very pretty phee- 
nomenon of the iodide of mercury was first observed by Mr. 
Hayes, an American chemist, who published it fourteen years 
ago in Silliman’s Journal. By all means then in future let it 
be ascribed to Mr. Hayes. It is to be regretted that his 
claim was not sooner mentioned; but I suppose that no one 
was aware of it. 
I have referred to the page indicated of the American jour- 
nal, but I find nothing more there that has reference to this 
particular subject. Mr. Hayes does not appear to have no- 
ticed the definite form and rectilinear boundaries of the scarlet 
portions of the crystal; which fact adds something, I think, 
to the argument, that the change of colour is owing to mole- 
cular displacement, and not to the loss or gain of any sub- 
stance whatever. 
With respect to the very different phenomenon seen in 
the iodide of lead, 1 believe that if any chemist would take 
the trouble to ascertain exactly what passes during its rapid 
transformation, this could not fail to be a valuable contribu- 
tion to science; for at present it remains one of the most 
enigmatic facts in crystallography. 
London, March 11, 1843. H. F. Tarzor. 
LIV. Notices respecting New Books. 
An Introduction to the Study of Chemical Philosophy, being a Pre- 
paratory View of the Forces which concur to the Production of Che- 
mical Phenomena. By J. Freperic Daniexx, For. Sec. R.S., 
Professor of Chemistry in King’s College, London, &c. &e. 
4 Wrap author of this volume informs us in his preface to the first 
edition, that “ the origin of his work was a desire to present to 
students of chemistry an elementary view of the discoveries of Dr. 
