Knight's American mechanical dictionary : a description of tools, instruments, machines, processes and engineering, history of inventions, general technological vocabulary ; and digest of mechanical appliances in science and the arts . aving !t very small aperture at one end, iuto which wasinserted a miuute globular leus, which allowed only Vstiw^^^part of the solar disk to be seen, lie found that this small por-tion atVorded a ligLit equal to that of the star, aud therefi-omconcluded that the star was 27,664 times more dist-int than thesun; a conclusion from arbitrary premises. 2. One pholume
Knight's American mechanical dictionary : a description of tools, instruments, machines, processes and engineering, history of inventions, general technological vocabulary ; and digest of mechanical appliances in science and the arts . aving !t very small aperture at one end, iuto which wasinserted a miuute globular leus, which allowed only Vstiw^^^part of the solar disk to be seen, lie found that this small por-tion atVorded a ligLit equal to that of the star, aud therefi-omconcluded that the star was 27,664 times more dist-int than thesun; a conclusion from arbitrary premises. 2. One pholumeitr of Count Itumford consisted of a numberof pieces of dimmed glass, which were placed iu succession iufront of the iigJt until the li^ht was no longer visible. Tuerelative intensity was determined by the number of pieces re-quired to m ike the light disappear. Fig. 368:i shows a tube a inclosing an inner sliding tube b,one half of which is graduated and the otaer has an opeuiugfor the insertion of a slip of glass g-, photographically gradu-ated in color from transparency to total blackness. The outer tube is held so that the aperture c is presented tothe light, wlxich passes through the slip ^aud is reflected to the Fig Photometers. 0 eye end of the tube by the mirror within it. The diftancewhich the tube must be drawn out to render tlic light visiblemeasures its intensity and is indicated by the graduations. 3 The photometer of Celsius consisted in observing thegreatest disUmce from tin <\e. on which small circles pamtedon paper were distimtlv visihtc in different lights. 4. Count Ilumford, lrir<tli-y, Houguer,and Lambert all gavetheir attention to this subject and eUcited tlie following prin-ciple : — Though the eye cannot judge of the proportionate force ofdifferent lights, it can distinguish with considerable precisionwhen two similar surfiices presented together are equally illu-minated, or when the shailows of an opaque object thrown uponthem by different
Size: 1262px × 1979px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjectin, booksubjectmechanicalengineering
