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THE ALUMNI JOURNAL. 



camera consists of — a modification of it. 

 Now, when the facts ascertained by 

 Scheele, i. e. t the action of light upon 

 silver chloride — turning it black and 

 producing gas (and by the way Scheele 

 never found out what this gas was and 

 to-day it is a matter of controversy and 

 a problem among chemists) — with the 

 facts ascertained by Scheele, in regard to 

 the action of light Thomas Wedgewood 

 and Vueder made pictures, in 1802. 

 These pictures were very peculiar. 

 They spread upon paper and upon 

 glass plates that had some gummy 

 material upon them silver chloride — as a 

 precipitate, and then they set their sub- 

 jects up, so as to get a profile shadow 

 with a strong light upon the surface. 

 Now, where the light passed, of course 

 they got a black mark upon the silver 

 chloride, but the silhouette of the face 

 was in white. Now, that was very 

 remarkable, because they got some very 

 remarkable pictures of which drawings 

 were made. They were white silhouettes 

 on a black background, but remember 

 that the pictures that were thus made, 

 the white silhouettes (if I may use the 

 term) were made by the action of some 

 light. If you wanted to copy them you 

 had to copy them out of the light ; other- 

 wise the whole mass would get black, 

 and that was the difficulty. In other 

 words, the white impression could only 

 be examined by candle or some other 

 weak light, and they ultimately became 

 shrouded in darkness and were lost — so 

 we have now none of those pictures. 



While they were experimenting in 

 England, a man named Niepse, a 

 Frenchman, was at work upon the same 

 subject — the action of light upon various 

 materials, but in a somewhat different 

 direction. In 1813, or probably before 

 that time, he discovered that certain 

 kinds of bitumen were soluble in oil of 

 lavender, and that when you exposed 



these pieces of bitumen to some light the 

 oil of lavender would not dissolve them 

 any more. He conceived the idea (how, 

 is not on record), but he thought that if 

 he could coat plates with this bitumen and 

 then expose them to light in a camera he 

 could get a picture upon this bitumen, 

 and where the light had acted the 

 bitumen would be insoluble in oil of 

 lavender. Where the light had not acted 

 that he could dissolve it out. He pro- 

 ceeded to do this, and succeeded in getting 

 pictures upon metal plates. He then, 

 afterwards, etched the plates and thus 

 got a perfect drawing or picture. So he 

 used it simply as a means to Droduce a 

 picture by etching. Now, understand, 

 using the camera, he obtained an impres- 

 sion upon metal plates coated with bitu- 

 men. After exposing the plates in the 

 camera he washed them in oil of lavender 

 and then an etching fluid, and cut the 

 impression into the matter and then they 

 were printed. Some of these pictures are 

 still in existence, they say. I have never 

 seen any of them . Alter a time the plates 

 were cleaned, and by the help of an etch- 

 er's tools or an engraver's tools they were 

 cut still deeper and made very good en- 

 graving plates ; so that his object was 

 not simply to etch them but to produce 

 plates for engraving. 



While this was going on Herschel made 

 an important discovery in 1819, and that 

 was that chloride and bromide and iodide 

 of silver were not soluble when blackened 

 by light. He found that after you had 

 exposed these materials to the light — 

 this silver iodide, bromide or chloride — 

 and had washed all these with hypophos- 

 phite of sodium, they would not dissolve. 

 That was important. That made it pos- 

 sible to preserve the silhouette pictures 

 devised or discovered by Wedgewood and 

 Vueder. Therefore, after exposing the 

 plates in the camera, as did Niepse, the 

 Frenchman, he washed them in a solu- 



