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POPULAR SCIENCE REVIEW. 
kept without the action of the developer for six months after the exposure 
the lines would have been equally invisible. It was not time, which pro- 
duced the image, and I think the question of physical versus chemical action 
is in no way touched by the fact. It seems to me that the iodide of silver 
on the plate was altered by light so as to he acted upon by the developer ; 
that the developing action was not continued sufficiently long under the in- 
spection of the operator for all the details to be produced, but the plate being 
considered useless was put away with some of the developer adhering to it, 
which, acting slowly upon the already altered iodide of silver, gradually 
continued the light’s action. This fact proves, I think, if it proves any- 
thing, that however weak the action of light may be upon a plate, it may 
be rendered visible if you develope long enough.” It is giving M. Davanne 
excessively little credit to suppose that he overlooked the above extremely 
simple explanation of M. Magny’s u curious fact.” We think it exceedingly 
improbable that M. Davanne did not satisfy himself upon the above points 
before he plunged into print and asked for an explanation of a very different 
nature than that based upon the above assumption. 
The Tannin Process . — Better pictures than those produced by the Tannin 
process we have not met with. Therefore, in common with most other 
photographers, we were grieved and annoyed to read in the Journal of 
the Photographic Society an ill-judged editorial article strongly condemna- 
tory of the process, sneering at its author, and insulting the many able 
and eminent amateur and professional photographers, who practise it. The 
following quotation, as a specimen, will, we fear, not convey a very favour- 
able impression of its author’s good-nature or impartiality. “ To clear 
the ground of rubbish is at all times a step in the right direction. For this 
reason the almost total abandonment of the tannin process must result in good. 
This process has vexed and irritated photographers ever since its first appear- 
ance. The best pictures ever exhibited by it have been of that mediocre class 
which pleases none but those most easily pleased. Much time would have been 
saved to amateurs if the process had remained in the chaos from which it ap- 
parently sprung ! ” The editor of one of our contemporaries says : “We are a 
little curious to know how such earnest workers as Messrs. Mathew Whiting, 
Le Neve Foster, Jabez Hughes, Warwick, King, Major Russell, and nume- 
rous other gentlemen, whose names have been honourably and intimately 
associated with the practice of the tannin process relish the impertinences 
thus flung at them.” Several gentlemen who were on the Council of the 
Society sent in their resignation in consequence of this uncalled-for attack, 
protesting against the admission of articles into the Society’s Journal , which 
are injurious to its character and to the best interests of the Society; and 
a letter from one gentleman whose name was introduced in the article 
as antagonistic to the tannin process has been published, in which he says 
that he has abandoned every other process and given in his adhesion to the 
tannin as the best he can employ. 
Hardness as a defect in Photographs , has received attention at a meeting 
of the South London Photographic Society in a paper read by one of its 
Vice-Presidents, Mr. A. H. Wall, who pointed out that the excessive in- 
tensity of the illumination given by a lens must necessarily produce images 
very different from those seen by the human eye. The smallness of the 
