The Astrophysical journal . ted with a removable cap pierced with a mm circular apertureand covered with ground glass for use with daylight. When working with the con-stant acetylene light, the cap is removed and the burner instantly placed in position. SENSITOMETRY !37 TABLE IV Sky bright and sunny. Plate, Seed 27 Emul. 11168; Oct. 12, 1906 Plate No. Time of Exposure Position on Plate length of Remarks I I 2 3 3 4 4 IO A. :30 A. :15 A. M. 1 P. M. 2 P. :15 P. P. M. Upper halfLower halfUpper halfLower halfUpper halfLower halfUpper halfLower half 3 min. Blue with white cl
The Astrophysical journal . ted with a removable cap pierced with a mm circular apertureand covered with ground glass for use with daylight. When working with the con-stant acetylene light, the cap is removed and the burner instantly placed in position. SENSITOMETRY !37 TABLE IV Sky bright and sunny. Plate, Seed 27 Emul. 11168; Oct. 12, 1906 Plate No. Time of Exposure Position on Plate length of Remarks I I 2 3 3 4 4 IO A. :30 A. :15 A. M. 1 P. M. 2 P. :15 P. P. M. Upper halfLower halfUpper halfLower halfUpper halfLower halfUpper halfLower half 3 min. Blue with white cloudsBlue with white cloudsSlightly brighterSlightly brighterStill brighterIntensity about the sameSlightly dullerLight much weaker Two exposures on each plate. All four plates cut from one large plate. opacity-ratios are constant. Between i p. m. and 4 p. m. there is anindicated difference in light-action of 2I3=2-5 times, which allowsfor considerable fluctuation in light-value. But that this is by no o o. Q Exposure inpowers of i38 ROBERT JAMES WALLACE means a limiting value is shown by the parallelism of the curves inFig. g, which represent a difference in light-action of 23 3 or There is no difficulty in obtaining any amount of corrobo-rative data in this connection. It should be remembered, that with varied exposure andequaltime of development, we obtain, as the exposure is increased, an addition ,/ 2 -4 1 Fi£ ».9. 55Cu Q I .2 /< 1 ( / 0 i / Exposure ini 23456789 powers of 2 of an equal density (or fog) to the complete negative; but this increaseof density does not in any way alter the opacity-ratios existing betweenthe series of exposures on the same plate (throughout the straight por-tion of the curve), such opacity being governed by the development: SENSITOMETRY 139 there is no alteration in the gradation. Hence the curves of twodifferently exposed spectra would, as a whole, be parallel to each other,although the height of the ordi
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
