TRANSACTIONS OP THE SECTIONS. 105 



ADDENDUM. 



On Photography. By H. F. Talbot, Esq., F.R.S. 

 [Article omitted in its proper place, p. 37.] 



Mr., Fox Talbot said that he had made many experiments on sulphate of iron as a 

 photographic agent; attention having been called to the subject by Mr. Hunt. He 

 could not recommend the use of succinic acid. The same iodized paper as was used 

 in the calotype process, gave the best results. With this and sulphate of iron he had 

 obtained portraits in one or two seconds. 



This process, then, only differed from the calotype process in using sulphate of iron 

 instead of gallic acid to bring out the picture. He therefore objected to the introduc- 

 tion of a new name ; for since otiier substances (such as tea, tannin, &c.) possess this 

 bringing out property, and probably many more will be discovered in future, each of 

 these would require, upon the same principle, to have a separate name, which would 

 be productive of inconvenience rather than advantage. 



2. The spontaneous development of pictures in the dark, was a thing of constant 

 occurrence in the calotype process (which indeed was first discovered in that man- 

 ner). Moreover, when the io-gallic paper, formerly described by Mr. Talbot, is em- 

 ployed for calotyping instead of iodised paper, no second wash is required to bring 

 out the pictures, which develope themselves spontaneously after removal from the 

 camera; and therefore the process which Dr. Woods recommended was not new in 

 this respect. The time necessary for the complete development of the pictures varied 

 considerably, according to circumstances, from a few seconds to one or two hours. 



3. In reference to Prof. Grove's communication, Mr. Talbot reminded the Section 

 of the account he had formerly published of the positive variety of the calotype process, 

 in which an iodized paper not really but virtually darkened by light, is again virtually 

 whitened by exposure to light in the camera, the final result being brought out by 

 gallic acid in the usual way. By operating with these virtual papers, the time re- 

 quired for a positive camera picture was greatly shortened. Still however it was ten 

 times longer than for the negative process, and therefore there was room for improve- 

 ment in this branch of photography. lYie positive camera pictures are very beautiful, 

 having of course all the delicacy of first impression, which is lost in transferring the 

 image to a second sheet of paper. 



On Mineral Springs and other Waters of Yorkshire. By William West. 



Entering the county from the south, we have at Birley Spa, Hackenthorp, four miles 

 from Sheffield, a slightly saline spring, and a saline chalybeate ; the former contains 

 per imperial gallon — 



Sulphate of soda 7-44 



Chloride of calcium I'Ol 



Carbonate of lime -55 Total... 9 grains. 



This supplies hot baths, and a remarkably commodious plunge bath. The chalybeate 

 contains — 



Sulphate of soda 40 



Sulphate of lime 22-5 



Carbonate of lime '5 



Protoxide of iron 4- Total... 67 grains; including 



The two are within a very few yards of each other. a minute trace of magnesia. 



On the gritstone moors, to the west of Sheffield, I found springs and streams of the 

 purest natural waters I have ever examined ; the proportion of solid matter was less 

 than two grains per gallon, and some of the substances present required for their de- 

 tection that the water should be much concentrated ; when this was done their nature 

 was found to be as complicated as in ordinary waters, sulphates, muriates, and car- 

 bonates, with lime, soda, magnesia and iron, for bases. 



The waters of Askern near Doncaster, have long enjoyed some celebrity, and se- 



