326 The Rev. J. B. Reade on some- early 



the gas thus produced had its origin deep seated beneath the 

 London clay, showiug that volcanic force, although in a moderate 

 degree, has exerted an influence in this locality since the depo- 

 sition of the coralline crag bed. Whether these fumeroles or 

 mofettes were formed only at the period immediately antecedent 

 to the present epoch, is, perhaps, difficult to determine ; they 

 might have existed during the latter portion of the time when 

 this bank was under formation, before it was ever elevated above 

 the sea : I am inclined to attribute them to the time when the 

 gravelly and sandy deposit of the red crag overlaid this coral 

 bank before the face of the country was modified into its present 

 form. They are, however, here brought forward to show the 

 great probability that these calcareous rocks have been acted 

 upon by gases rising from below as well as by acids in a down- 

 ward direction ; and although the surface of the chalk, as well as 

 the crag, is corroded in most places, denoted by the funnel- 

 shaped depressions beneath the superficial soil, there have not 

 been recorded, that 1 am aware of, such marked evidences of 

 upward action in any other rock in this country from the cre- 

 taceous period to the present time. 



XLVIII. On some early Experiments in Photography, being the 

 substance of a Letter addressed to Robert Hunt, ^sg'. By 

 the Rev. J. B. Reade, M.A., F.R.S. 



Stone Vicarage, Aylesbuiy, 

 My dear Sir, February 13, 1854. 



IN giving you the information you require respecting my 

 early researches in photography in 1836 and following 

 years, 1 may assume that you are already aware, from my letter 

 to Mr. Brayley of March 9, 1 839, and published in the British 

 Review for August, 1847, that the principal agents 1 employed, 

 before Mr. Talbot's processes were known, were infusion of galls 

 as an accelerator, and hyposulphite of soda as a fixer. 



I have no doubt, though I have not a distinct recollection of 

 the fact, that I was led to use the infusion of galls from my 

 knowledge of the early experiments by Wedgwood. 1 was aware 

 that he found leather more sensitive than paper; and it is highly 

 probable that the tanning process, which might cause the silver 

 solution to be more readily acted upon when applied to the 

 leather, suggested my application of the tanning solution to 

 paper. 



In your own history of the photographic process, you say 

 '•' the discovery of the extraordinary property of the gallic acid 

 in increasing the sensibility of the iodide of silver was the most 

 valuable of the numerous contributions which Mr. Talbot has 



