I could tell you a good deal more about this subject, but there is only one other thing I would now like to mention. Some of you, I suppose, have heard a great deal about taking photographs in colors. We are very near it. They have produced in France, Germany and England pictures of the spectrum in the silver salts: that is to say, with the colors of the spectrum. They are very weak and have to be looked at in a certain light. They are the result of interference of the thin films. We are doing something more important. We are learning to make the whole spectrum. For example, we can to-day get just as good an impression upon silver salts with a red light as Scheele did with a violet light in 1774. That leads to what is called ortho-chromatic photography, that is photography that will give us every color in the spectrum. It has been found possible to make pictures in certain colors. A long time ago, the spectrum was separated into three colors, red, yellow and blue of certain kinds. Now, if you take a picture in a red light of a certain character, and another of the same subject in a yellow light of a certain character, and another in a blue light of a certain character, you have three negatives. You can make three negatives, one of the red light, one of the yellow light and one of the blue light. Now, by taking pigments and printing in a press like a lithographic press, you can make a red positive from the red negative, and a blue positive from the blue negative and a yellow positive from the yellow negative, and in that way you may get three impressions, which is the result in the same colors. You must not stop there, however. There is a certain amount of shadow, and the result of it is that they have to what they call “over-lay,” taking the three colors separately and superimposing them in printing. Remember, the red parts of the picture are taken with the red light. That is, suppose you put a red piece of glass in front of your camera, then only the red parts of the picture pass through to the sensitive plate. Then repeat the operation with the blue glass and the yellow glass, and the result will be as above. Now I hope I have not bored you by any profuse details. I did not intend to. I only tried to interest you in one of the most important inventions of the Nineteenth Century. The steam engine, the telegraph, the telephone and the photograph are four of the grand inventions which the century has produced, and I think every intelligent person should learn something about them. I am afraid that I have had too little time to do the subject justice. You can understand how much more there is behind this superficial view. I only have to thank you for your very kind attention. The Alumni Journal Published under the auspices of the Alumni Association of the College of Pharmacy OF THE CITY OF NEW YORK,