The advance of photography : its history and modern applications (1911)

Record Details:

Title:
The advance of photography : its history and modern applications
Date:
1911
Publisher:
London : K. Paul, Trench, Trübner & Co., Ltd.
Volume:
The advance of photography : its history and modern applications
Leaf #:
000400
Language:
English
Subjects:
Motion Pictures, Motion pictures--Technology
Collection:
Books
Format:
Books
Contributor:
Media History Digital Library
Sponsor:
Media History Digital Library
Coordinator:
Media History Digital Library
Description:
Date Added:
November 02, 2023
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320 THE ADVANCE OF PHOTOGRAPHY Pairs of plates are used, one being ordinary and the other isochromatic. The former plate has a maximum of sensitiveness at about a wave-length of X4000, while in the case of the latter the maximum sensitiveness occurs about A5550 in the plates used, therefore it follows that a star giving a maximum radiation in the blue or violet will produce a more marked effect upon the former, while one the maximum for which occurs in the yellow or red will appear stronger upon the latter. The more intense the colour of the star, the greater will be the difference of magnitude on the two plates, so that by this means a measure of the colour intensity can be obtained quite as accurately as the measure of the magnitude. The magnitudes are obtained from these plates by measuring the diameters of the discs under the microscope, and reducing the results by means of the formula : — magnitude = a — b V/D,in which D= diameter of the disc, a=a constant for each plate depending on the exposure, and found for each plate by using the visual magnitude of the white stars; 6=a constant depending upon the emulsion and conditions of development. It is also found that definite colour intensities correspond in general to definite spectral types, and this of course furnishes a means of determining the spectra of stars which are too faint for ordinary spectroscopic analysis.