Space or lack of it does not allow us to describe how the microscope may be and is applied to other manufactures, even the miller uses the instrument, for it will tell him if his flour is of pure wheat, and in this manner. He puts a little flour in a drop of water on a slide and covers with a cover slip; then, for a moment or two, he rubs the cover glass to and fro over the water and flour and examines his specimen under the microscope. If his flour be of wheat, he will see fairly stout spindle shaped strings, if it be of rye no strings appear, whilst maize flour gives very small strings. These are called gluten strings and wheat is very rich in gluten. CHAPTER XX THE MICROSCOPE AND CAMERA ALLIED Photography is such a popular hobby in these days, that the enthusiast who possesses both camera and microscope, is certain, sooner or later, to wish to take permanent records of some of the beautiful objects revealed to him by the latter instrument. The production of high-power photo-micrographs, as the pictures of highly magnified objects are called, can only be carried out by those who are skilled in the use of both camera and microscope and are possessed of considerable patience. There is nothing to prevent any amateur photographer who possesses a bellows camera--box cameras cannot be used for this work--from producing excellent low-power photo-micrographs, that is to say pictures of objects less highly magnified. It may be disappointing to learn that a microscope is not necessary for this work. The requirements are, a camera which will open out to a considerable extent and a short focus lens. Before we show how the pictures may be taken, we must be quite clear what is meant by a short focus lens. There are various ways of measuring the focus of a lens; in the case of a single lens the operation is fairly simple, but single lenses are made of one glass and most camera lenses are built up of several pieces of glass, then it is much more difficult to measure the focus quite accurately. For ordinary purposes and for our purpose, it is only necessary to know the focus in round figures and to do so we open up the camera and focus some distant object on the ground glass, then the distance in inches from the back of the lens to the ground glass will give us very nearly the correct focus, or as it is often called focal length, of our lens. Suppose we focus on a church steeple a mile away and then find that a space of five inches separates the back of our lens from the ground glass, the lens is of five inches focal length.