A treatise on the microscope : forming the article under that head in the seventh edition of the Encyclopaedia britannica / by Sir David Brewster.

  • David Brewster
Date:
1837
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on the microscope : forming the article under that head in the seventh edition of the Encyclopaedia britannica / by Sir David Brewster. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

    44/242 (page 32)
    it is seen is equal to the focal length of the lens; and as apparent magnitude of objects is inversely as the dis- tance-; at which they are seen, we have only to divide the 'listancc, five inches, by the focal length of the lens, in order to know its magnifying power, or its apparent magnitude when seen through the lens. The following table shows the magnifying power of lenses of all focal lengths, from 5 inches up to the 100th of an inch, and is applicable to all lenses, of whatever sub- stance they are made. Focal Length. Power. Focal Length. Inches. Inches. 5 1 i T6 2 tV \i & 4 5 23 3 6f ~t 1 2 10 35 X 15 I 40 1 20 1 33 k 25 1 37) 1 30 J 5 5 j 7 35 I ITo is | 40 i ¥ 45 To j To 50 l 73 l 55 l TTo 5 ] 2 60 i ] 65 t : 2 70 75 • 17 i no Magnifying Power. 80 85 90 95 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500