The idea is this: That you make a gelatine mixture of a certain strength--the proportions required a certain amount of soft gelatine and a certain amount of hard gelatine. Into that gelatine you pour, with constant stirring; you pour a mixture at the same time--some particular bromide, generally bromide of potassium and nitrate of silver--in a very thin stream and keep it thoroughly stirred up. If you go too fast, you will not get the right result; but the result is, when you get through and do it right, you get a beautiful milky fluid, and that fluid contains bromide of silver in a wonderful state of suspension--very thin--and it remains suspended in this fluid. Now let that set--this cream or “emulsion,” as they call it--and you have as a result iodide of silver and iodide of potassium. You let the emulsion set and it produces a jelly, that jelly is then cut up into shreds, rubbed through a sieve or something of that kind to make it thoroughly divided, and washed thoroughly with water. Having done that it can be melted, and if you melt it and heat it to a certain temperature, there does not seem to be any limit to the sensitiveness of the material. If you use it cold it requires a second or two to produce a picture. If you cook it, however, you will find that it will become more and more sensitive to light, until it is actually possible to take a picture of a projectile traveling four hundred metres per second. I have such a picture. The only trouble is that some of the plates made are so sensitive to light that we cannot get a light non-active enough to develop them. Having these bromide plates then in the camera--this sensitive material coated on these glass plates in the camera--you have got to be very careful that the light does not get to them. The consequence is that the plate holders are made with extreme care.