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XV. On the coloured Rings produced by Iodine on Silver, 
with Remarks on the History of Photography. 
By H. F. Tarzot, Esq., F.BS., Se. 
To the Editors of the Philosophical Magaxine and Journal. 
GENTLEMEN, 
IN your Numberfor December 1842, you haveinserted an in- 
teresting account of some experiments by Dr. Waller on co- 
loured films :—in which account, however, I have noticed with 
some surprise what is there stated to be a new method of 
making coloured rings, like those generally known under the 
name of ‘* Newton’s coloured rings,” on many of the metals, 
“In order to procure these coloured rings,” says Dr. 
Waller, “we have but to place a piece of iodine on a well- 
polished surface of silver or copper, and in a short time we 
find around the iodine a series of coloured zones of the various 
tints of the spectrum.” In the next page he adds, “ the ac- 
tion of light on the different colours is very interesting; the 
most correct way of studying this, is to protect one half of a 
system of coloured rings by an opake screen, while the other 
half is exposed for a short time to the influence of the solar 
rays. The golden zone...... is converted into a beautiful 
green,” &c. &c. &c. 
Now, since the History of Photography will probably be 
written some day or other, it is desirable that the different 
phzenomena discovered should be ascribed to their first obser- 
vers, with as much attention to accuracy as possible. 
As this is in most cases the only reward of scientific re- 
searches, justice requires that it should be scrupulously ad- 
hered to, and if by accident a mistake occurs it ought to be 
speedily rectified. 
Give me leave therefore to state that this method of form- 
ing Newton’s rings was first discovered and published by my- 
self; and that I particularly called attention to the beautiful 
phenomenon which occurred when the rings were formed on 
silver, namely, that they were sensitive to light, and when 
held in the sunshine transmuted themselves into other co- 
lours,—a fact until then quite unexampled in Optics. 
I brought forward the matter at the Birmingham Meeting 
of the British Association on the 26th of August, 1839, and 
a full report of it will be found in the Athenzeum for that year, 
page 643, and in the Literary Gazette, page 546*. 
From the ample publicity which I gave to it at that time, 
* An abstract of Mr. Talbot’s communication was afterwards given in 
the Report of the Ninth Meeting of the British Association, Transactions 
of the Sections, p, 3.—Ep. 
