This wet plate process continued from 1851 to 1871, about twenty years. I have the pleasure of showing you an amateur outfit for this process, used in 1860 to take to the Rocky Mountains (exhibiting it). That is an amateur outfit carried over the Rocky Mountains in 1860 to take pictures. Here is the old tank that carried the water. Here are some of the bottles of chemicals, and the way it was managed was this: This was hooked up, on the end of these sticks. This was the black cloth used as the developing room by the operator. Here is a little window with yellow glass to develop the pictures. The plates and bromide of silver was carried in these two boxes. That was carried on top of the mule and the boxes on the sides of the mule, so that he had a pretty good mule. Now, to-day we do the same work with that apparatus (exhibiting apparently a Kodak), and a great deal better work it is. In 1871 a more important revolution took place even than the wet plate process or the daguerreotype. Many efforts had been made to overcome the use of the wet plate--the plate wet with nitrate of silver, and some of the efforts were very successful but usually troublesome. The plate was kept moist in a variety of ways: by honey, by tea, by infusion of tea, by beer, by coffee, and a multitude of all the funniest concoctions you could think of, but the process was destined to fail. In about 1870 it was conceived that you could make an emulsion of these peculiar compounds of silver--these sensitive silver compounds--that you could make an emulsion that you could pour upon the plate and produce a picture just when you pleased, and it was found that by mixing the chloride that produces the sensitive material in one portion of your collodion and putting nitrate of silver into another portion of the collodion, in certain proportions, you could produce a collodial emulsion. They had to be mixed in just exactly the right proportions, so as not to have an excess of nitrate of silver or an excess of bromide. But that process failed and only lasted a few years; although I have here one of the plate holders used by such a process. This was between the time of the wet plate process and the modern dry plate, when they used collodial bromide emulsion. It was a kind of a compromise between the wet plate and the dry plate. In 1871, Dr. R. L. Maddox, of Bath, England, had the idea that he would use gelatine, instead of albumen or collodion, as a vehicle to hold these silver salts upon the glass surface, and he found, among other things, something that surprised him--that when he put the silver salts in to contact with this gelatine they became wonderfully more sensitive than ever before.