Proceedings of the Physical Society Volume 12

Proceedings of the Physical Society Volume 12

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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. 1894 edition. Excerpt: ... to bright. Before I had heard of this modification I had tried vertical bars or slots and perforated screens. The photometer is shown in fig. 2. It consists of a box mounted on a sliding-carriage on a photometer-bar. A slotted screen and a plain screen are fixed inside, and are observed through an opening from the direction C. The lights fall on the screens through two openings from the directions L and L1. The lights are arranged exactly opposite the middle of each side opening, and not in the plane of the photometer-bar as is usual. The lower edge of the front opening or diaphragm carries a sight or pointer, and the back screen is provided also with a pointer, preferably at its upper edge. The photometer may be examined from a distance, say six or eight feet, and moved by cords. The two sights should be brought in a line with each other, and the carriage is to be moved until the band of uniform tone is bisected by the pointers. If the carriage be moved slowly it will be seen that the band of uniform tone remains fixed relatively to the scale on the photometer-bar. Readings might be taken by noting the position of the band over the scale, but I prefer to follow the usual custom in photometry, and to keep the scale hidden until an adjustment has been made, to avoid any bias. The operation of estimating the bisection of the band by the pointers is, I think, easier and therefore more conducive to precision than the estimation of the similarity of two images as in the Bunsen, or of two tones as in most other photometers. I will now give details of the development of this photometer for the guidance of those who may wish to construct them. Perforated zinc of the ordinary pattern having holes about 0'08 inch diameter and % inch pitch, more

Product details

  • Paperback | 150 pages
  • 189 x 246 x 8mm | 281g
  • United States
  • English
  • black & white illustrations
  • 1236802934
  • 9781236802934