346 THE BEGINNINGS OV PHOTOGRAPHY. 



Chisolm, as Litchtield spells it) had a g-reat deal to do with the educa- 

 tion of young- Tom. He was a good chemist, a man of education, and 

 at least something of a classical scholar, and the bo}^ seems to have 

 received nmch of his scientific and classical training from him, and 

 when at the university corresponded freely with him, chiefly on chem- 

 ical topics. He no doubt also assisted him in his early experiments. 

 This connection of Chisholm, first with Doctor Lewis and the photo- 

 chemical experiments recorded in the Commercium Philosophicum 

 Technicum, and then with the Wedgwoods, throws a good deal of 

 light upon the probal)le origin of Tom Wedgwood's photographic 

 experiments, and it is possible that if an}^ of the correspondence 

 between Tom Wedgwood and Chisholm, or any of the hitter's manu- 

 script notes, are still available, some valuable information on the 

 subject may vet be obtainable. 



DOCTOR TRIESTI.EY. 



In 1772 Dr. Joseph Priestley pul)lished his valuable History of Dis- 

 coveries relating to Light, Vision, and Color, and it is interesting to 

 note (p. 378) that he was a believer in the theor}^ that light was a real 

 substance, consisting of particles of matter emitted by luminous bodies, 

 and considered that this view was favored by experiments demonstrat- 

 ing that the color and inward texture of some l)odies are changed by 

 exposure to light. He notes Duhamers researches on the purple 

 color extracted from a shellfish found in Provence, which is developed 

 by sunshine; also Beccari's experiments with luna cornea, alread}- 

 mentioned. With regard to this he remarks that it does not appear 

 that Beccarius knew on what ingredient in the composition the change 

 of color depended, and then he fully describes Schulze's experiments, 

 which prove it to have been the silver. Although Doctor Lewis's 

 book is mentioned in the list of authorities consulted by Priestley in 

 the preparation of his history, he makes no mention of his chemical 

 investigation of Schulze's experiment, but- goes on to discuss the 

 further experiments of Bonzius and Beccarius on the action of light 

 on ribbons, etc.; but these do not concern us at present. 



In connection with Priestley it may be noted that Josiah AYedgwood, 

 the father of Tom, was a subscriber to this book of Priestley's, and 

 we may agree with Miss Meteyard that it was not unlikely that young 

 Wedgwood would knov/ the book, especially as he was interested in 

 questions l)earing on light and heat. Moreover, Mr. Litchtield men- 

 tions (op. cit., p. 19) that while working at the long series of experi- 

 ments descril>ed in his two papers of 1701-92 Tom Wedgwood was 

 corresponding with Priestley, who was an intimate friend of the family, 

 and if he were working at photography at the same time it is not 

 improbal)le that his attention would have been drawn to Schulze's 

 experiment, even if Chisholm had not already told him of it. 



