The beginning of the daguerreotype flourished only a short time. While Daguerre and others were working at the daguerreotype, Fox Talbot, a rich Englishman, took up the subject from another point of view. He conceived the idea of making a negative. Of course, every picture you took by Daguerre’s method you had to make a sitting for it. Such are the pictures up in the School of Mines of William Lloyd Garrison and Daniel Webster. They had to sit right down in front of the box, and copies could not be had. That was the trouble with the daguerreotype. You had one picture for every sitting. To make the difference between the positive and negative more clear, I have brought here to show you to-night (producing them) some positives and negatives printed on the same piece of paper. When the picture comes out of the camera and the plate is developing (exhibiting it) that is what it looks like--where the light struck all the light parts of the picture are black, and where the light did not strike all the black parts of the picture are white. If I take the same surface, containing the bromide of silver, iodide of silver or chloride of silver, and place it underneath that and expose it to the sunlight, where the light strikes through it will produce black, just as in the original object, and when I get through I get the positive. So there is a negative and there is a positive from the same picture. Now, that was Fox Talbot’s idea. He says “If I can do that, I can make pictures _ad libitum_.” With this object in view he coated paper with silver chloride. He exposed it then in the camera, fixed it in a solution of salt--common salt or iodide of potassium--and when he got through the picture was a permanent one, because the iodide of potassium dissolved out the white parts that were not affected by the light. From this negative he obtained other prints. Now, various modifications of Fox Talbot’s process, were brought out, and a man named LaGray, I think (or at least it was just about the time he lived) conceived the idea of making these pictures more transparent by waxing them. That was the first good negative we had. It was a modification of Fox Talbot’s idea, only he waxed the paper. Then about the same time it was found that a mixture of chloride of iron and cyanide of potassium, when mixed together were acted upon by light. Herschel discovered this, and that was the way we obtained the blue print, which is far older than the photograph. Sir John Herschel found that a mixture of chloride of iron and cyanide of potassium, when exposed to sunlight made Prussian blue. So that if you take paper and coat it with this mixture and then expose it under a negative you get a blue picture.