Publications of the Allegheny Observatory of the University of Pittsburgh Volume 2

Publications of the Allegheny Observatory of the University of Pittsburgh Volume 2

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1912 edition. Excerpt: ...screw-readings and in the angle 0 all that is necessary to state very precisely through what angle the plate has been turned. The screw is a left-handed one turned upon a hardened steel shaft 59 cm. long and 30 mm. in diameter. Of this length 35 cm. is threaded with a one millimeter pitch. The micrometer head and the handle for turning it are at the left hand of the observer instead of the right. This little departure from the usual arrangement adds much to the convenience of measuring without detracting in the least from the accuracy, the observer's right hand being thus free for recording. The diameter of the micrometer head is unusually large (15 cm.), so that one micron on the plate corresponds to nearly half a millimeter on the head. The latter is graduated into 200 spaces, each of which corresponds to five microns. The readings may therefore be made by estimation to half a micron, though for most work we have been content to record the nearest micron. In order to move the microscope rapidly across the plate a set of change-gears G with the ratio of five to one is installed at the left. One turn of the gear handle The small screw engine with which we measure the Mellon Spectrograms is reversible and either hand may be employed for making the settings. All the observers who have used this engine have found that, after very little practice, settings can be made with equal facility and with equal accuracy by the left hand. moves the microscope five millimeters; the examination and the adjustment of the plate are thus considerably facilitated. This change-gear can be very easily thrown out of mesh and this is always done as soon as the observer is ready to begin definitive measuring; thereafter the screw is turned only by means of the...show more

Product details

  • Paperback | 50 pages
  • 189 x 246 x 3mm | 109g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236839218
  • 9781236839213