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THE ALUMNI JOURNAL. 



ing impressions by means of light was 

 very ancient. There was another French- 

 man, named Devique Delaroche, who 

 made a still more curious statement- In 

 1760 he wrote a book in which his hero 

 is wrecked upon a strange coast, and the 

 spirits of that place showed him how to 

 make pictures, as he called it, "painted 

 by nature." It is not quite sure what he 

 means, but his words are something like 

 these: "You know," says his guide, 

 "that rays of light are reflected from 

 different bodies and form pictures. The 

 spirits have sought to fix these pictures, 

 and have a subtle matter by which these 

 pictures are formed in the twinkling of 

 an eye. They coat canvas with this pe- 

 culiar matter, and hold it before the 

 object." The manner of holding it is 

 not stated. "The canvas is then re- 

 moved to a dark place and in an hour 

 the impression is dry and you have a 

 picture, the more precious in that no art 

 can imitate its truthfulness." These 

 words were written one hundred and 

 fifty years ago. This, as far as we 

 know, was purely imagination ; yet the 

 idea — the germ of photography — was 

 there. We shall presently see that this 

 flight of fancy on the part of Delaroche 

 was very near the truth, and foretold 

 what has since become possible, and only 

 a very short time after he said it. 



As time went on and observations of 

 men became more definite, we obtain 

 records of facts that were noted with 

 regard to the action of light upon certain 

 chemical compounds. You know those 

 old alchemists had queer ideas, one in 

 regard to their elixir of life, and another 

 that they could turn the baser metals in- 

 to gold. They discovered a material in 

 the silver mines of the Hartz Mountains 

 which they called " luna cornea." The 

 word luna was at that time applied to 

 silver. Luna cornea was horn silver — 

 what we know to-day as silver chloride. 



They noted that when this was first 

 brought from the mine it was white and 

 that after it had been exposed to the air 

 and the sunlight it turned black, and 

 they also noticed that it was only the 

 surface that turned black — that if they 

 scraped the surface off it was white un- 

 derneath. They also found that if they 

 kept it in the mine it did not get black. 

 This observation was made about 1550 

 by Frobrishes, one of the early workers 

 in chemistry ; but you must remember 

 that they were not studying the action of 

 light upon this substance. Their sole 

 object was the turning of the baser metals 

 into gold, and therefore they did not pay 

 much attention to this idea, although 

 this fact was placed on record. 



Some time after this we learn that a 

 German named Schultze made copies 01 

 drawings with a mixture of chalk and 

 silver nitrate spread on a level surface. 

 The time ot this is doubtful, but it was 

 probably about the year 1700. He passed 

 the light, as he says, through translucent 

 paper (made translucent with oil or wax), 

 and objects placed upon the paper left a 

 white impression on the mixture of chalk 

 and silver nitrate — or, as he called it, 

 "lunar caustic." This was in about 

 1700, as I said. About fifty years after 

 this time (and indeed it was a little more, 

 it was seventy years, in 1777) Scheele, 

 the Swedish apothecary's assistant, took 

 up the examination of this horn silver. 

 It seemed to him well worthy of study ; 

 and as the result ot his work he obtained 

 the first germs that led to the art of pho- 

 tography. But before Scheele could have 

 prosecuted his researches, and before 

 photography could make any important 

 advances, there were two other discover- 

 ies in science — and in optics particularly 

 — that had to be made. The first of these 

 was the decomposition of white light, by 

 Sir Isaac Newton, by which he obtained 

 the prismatic colors ; that is to say, the 



