> <.: =: *) 
a od OE 
95 
me to be strictly analogous to the above. If I comprehend your 
description, you use an iodised paper in which iodide of iron is em- 
ployed instead of iodide of potassium. 
‘* You may be quite right in attributing the effects to Electro- 
lysis, but then it follows that my Calotype process, with all its 
variations, must result from the same cause. 
* T am, Sir, 
‘* Your obedient Servant, 
‘“* H. Fox Taxzor. 
“Dr. Woods.” - 
‘** Lacock ABBEY, 
“18th March, 1845. 
**Sir,—TI have to acknowledge the receipt of your courteous 
letter of the 15th instant, upon which I beg leave to make a few ob- 
servations. In my Calotype process, iodide of silver is decomposed 
by the joint influence of light and a deoxydising agent (gallic acid). 
Mr.Hunt has shewn that sulphate of iron may be substituted for gallic 
acid, and he calls the process so altered Energiatype. But since tan- 
nin and other substances may also be substituted for gallic acid, each 
of these variations in the process would require, on the same princi- 
ple, to have a separate name, which would, surely, be inconvenient. 
In your method, iodide of silver is decomposed by the joint action 
of light and iron; the three reacting substances being the same as 
in Mr, Hunt’s Energiatype; and therefore, imperfect as the theories 
of photography confessedly are, I cannot persuade myself that a 
_ eatalytic action can take place in your process, unless it also takes 
place in the Energiatype and in my original Calotype process: I 
therefore cannot help considering these three processes as variations 
of the same, and not essentially different. I hope, however, you 
will not consider me as detracting in the least from your valuable 
labours: my remarks only refer to the nomenclature of the science. 
If I am not mistaken, the three methods I have named produce 
pretty nearly identical vesu/ts, though I speak from experience of 
only two of them, Mr. Hunt’s and my own. Both of these are 
nearly certain in operation, very rapid, giving a camera picture of 
a bright object in a second of time, and requiring no second wash 
if enough of the deoxydising agent is employed in the first wash. 
_ It is. customary to make the positive copies on a different paper, 
