GENTLEMEN, -l find in your issue of the 2nd inst. an article on the above subject by George F. Williams the said article abounding in errors, and I wish you to allow me space to point out a few of them. At its commencement the writer says-"In that article mention is made of some specimens on opal glass by Mr. Helsby, and I will now concisely explain the methods of producing them."

Now, if in giving these explanations, the writer wishes to convey to your readers the impression that he describes the methods employed by Mr. Helsby in producing his photographs on enamelled glass, I beg to state that such is not Mr. Helsby's process at all, and that in its most important points it is not even like it. The writer next mentions polished opal glass, and says that "photographers are mainly indebted to Mr. J. A. Forrest, of Liverpool, for its introduction." To this I demur, on the ground that we should "render unto Caesar the things which are Caesar's." I was present when Mr. Helsby suggested to Mr. Forrest the idea of polishing the flashed or opal side of opal glass, and the first lot of glass so finished was to Mr. Helsby's order; therefore, photographers are not mainly indebted, &c., as stated by your correspondent. Then, again, to call the said glass patent "plate opal," is simply a misnomer. Polished enamel glass would be nearer the truth.

Next the writer asserts what is incorrect in saying that "Mr. Helsby claims that pictures for viewing by transmitted light are also adapted for viewing by reflected light." Mr. Helsby never claimed any such thing; he, being an old professional, knows better than to say anything so absurd.

Then comes the ungentlemanly part of the article, viz.:-" Perhaps a better way than either of the above methods is to print a positive for reflected light on a piece of opal glass of an elliptical form," &c., &c. The invidious "perhaps," as though, the writer had of his own mental acuteness discovered a better way!--whereas, for some considerable time previous to writing the said "perhaps" he had been in the habit of visiting Helsby and Co.'s studio, and examining their new specimen portraits, which are of an elliptical form, and are mounted in a jewel case. I cannot but think that it would, without doubt, have been more honest on his part to have acknowledged it.-I am, yours, &c.,

Liverpool, December 7th, 1864.