THE ALUMNI JOURNAL. 



3i 



colors that we know as violet, indigo, 

 blue, green, and so on down to the red. 

 That was the first step. The next step 

 was the discovery by Baptiste Porter, an 

 Italian, in Naples, which preceded the 

 discovery of Newton (it was about 1590), 

 that a small opening in a dark chamber 

 produced an inverted image on the wall 

 of the chamber. So that between 1590 

 and 1666 Baptiste Porter and Sir Isaac 

 Newton paved the way for the researches 

 of Scheele upon the action of light upon 

 this simple substance, as they called it, 

 4 ' luna cornea' ' or chloride of silver. Now 

 Scheele, therefore, at his time, 1777, knew 

 of the discovery of the prismatic colors, 

 or the decomposition of white light by 

 Sir Isaac Newton, and he made the ex- 

 periment of submitting this horn silver or 

 silver chloride to the action of light after 

 the light had been passed through a prism 

 and he found the light as we know it to 

 consist of violet, indigo, blue, green, 

 yellow, orange and red. Placing the 

 silver chloride in this band of colors, he 

 discovered the important fact that in the 

 red rays the silver chloride received no 

 change — that there was no change made 

 in it. But, as he got along toward the 

 other end of the spectrum, and got into 

 the green and the blue and the indigo 

 and the violet, he found that the color of 

 the silver chloride changed much more 

 rapidly, and he found that the most 

 active in its effect upon the silver chloride 

 were the blue and violet rays. In addi- 

 tion to this fact he found that the light 

 discolored the silver chloride. Scheele 

 still further proved that the silver chloride 

 was decomposed by the light, and that 

 chlorine gas, or, as he called it, dephlo- 

 gistigated marine acid gas, was produc- 

 ed. He became acquainted with this 

 previously from his experiments on the 

 mineral braunstein with muriatic acid. 

 So that when he perceived the odor of 

 the chlorine from the decomposition of 



the silver chloride, he recognized the gas 

 at once, and he says : " When this silver 

 chloride turns black it gives out 

 chlorine," and that was a very import- 

 ant fact. At the red end of the spectrum 

 he found there was little or no effect up- 

 on the silver chloride. This was the 

 principle of the camera obscura, and the 

 principle of the camera obscura is the 

 the principle of the photographic camera 

 to-day. Practically the photographic 

 camera consists of a dark box, with a 

 hole at one end and at this end there is 

 a place to receive an image. Instead of 

 having a lens there in the front of the 

 camera, as was formerly the practice, it 

 is perfectly possible to get the picture 

 with a small opening, say an eighth or 

 sixteenth of an inch in diameter, and, 

 furthermore, that is the most perfect 

 picture you can get in a camera — a 

 picture without a lens. Now, that is a 

 strange statement, and perhaps in these 

 days it may appear a little wild ; but 

 (exhibiting a photo about 5x7) there is 

 a picture made with an opening not larger 

 than a pinhole, and it is a good deal bet- 

 ter than many of the pictures taken by 

 the amateurs to-day. This opening be- 

 ing so small necessitates a good deal of 

 time in the action of the light upon the 

 sensitive silver salts behind, and that is 

 the object of placing the lens there. By 

 placing the lens here, instead of having 

 a small opening, you make a larger open- 

 ing which collects the light in the same 

 manner, brings it to the focus and then 

 the rays diverge again and you get the 

 picture. Now, the rays as they pass 

 through the opening without a lens, be- 

 gin to diverge as soon as they are in the 

 camera, but with a lens there they are 

 brought together first and then cross and 

 then you get the picture. That is the 

 first step, then, in photography, the pro- 

 duction of images by the camera ob- 

 scura — and that is all the photographic 



