Index to the Harvard Annals

Index to the Harvard Annals

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1917 edition. Excerpt: ... objective was focussed by means of a screw to throw up an enlarged image at a distance, where it could be received on a photographic plate. The was sunlight. It was hoped that the focus having been properly obtained for one plate, into contact with the rim of the cup carrying the objective. This hope proved futile owing to the slight irregularities or lack of flatness occurring in the surfaces of the plates to be enlarged. Therefore, it was necessary to resort more or less to individual focussing for different plates. Perhaps this will not appear of supreme importance when we consider that the length of exposure and the duration of development of each plate also has a distinct bearing on the resulting size of image. The microscope objective not being corrected for photographic rays, it was found that the plate must be set at some distance from the visual focus. The amount by which the photographic differed from the visual focus could be readily determined by experiment. For a few plates, however, a different scheme was adopted, which consisted in using yellow light and yellow sensitive plates. Yellow light was obtained by placing a yellow screen between the apparatus and the source of light. This method had the advantage not only of using monochromatic light, but light of the wave length for which the objective had been corrected. Twelve enlargements of fifty times are presented in Plate I. The data respecting them will be found in Table I. The successive columns give the number of the figure, the name of the instrument, the scale of the original plate, the scale of the enlargement, the designation of the original plate, the date when it was taken, and its exposure in minutes. The exposure...show more

Product details

  • Paperback | 52 pages
  • 189 x 246 x 3mm | 109g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236487060
  • 9781236487063