Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: MEASUREMENT OF THE GRAINS In any investigation into the microscopical appearances of starch grains it was clear to me that one of the fundamental and most important points was to obtain accurate measurement of the various grains. Here again microphotography was of great value, as by taking a negative of a micrometric scale magnified k times it served for measuring all starch grains under the same conditions of objective, ocular, and tube and camera lengths. From my previous experience of microscopic methods I had no hesitation in employing for this purpose the stage micrometer in preference to the micrometer eyepiece, and in adopting the micrometer scale, divided into parts of a millimetre, in preference to one divided into parts of an inch. Had I used the micrometer eyepiece it would have had one great advantage: viz., I could have photographed the divisions on the same negative and at the same time as the starch grains. There were, however, three drawbacks to this method, the first being that I could not have employed the projection ocular, the second that the divisions of the micrometer eyepiece were not sufficiently fine for my purpose, and the third that the divisions themselves would interfere with thatclear view of the whole ' field' of the microscope which I considered at least advantageous, if not absolutely necessary. Having come to the conclusion that accurate measurement of the starch grains was an essential element in this investigation, I first exposed a plate, with the view of getting a negative of a stage-micrometer divided into hundredths of a millimetre. With regard to the magnification, I had previously made experiments in order to find what appeared to me to be the most suitable camera length for the larger starch grains, by projecting images of these gra...