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Image from page 496 of “The Bell System technical journal” (1922)
Image by Internet Archive Book Images
Identifier: bellvol18system00techniamerrich
Title: The Bell System technical journal
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company
Subjects: Telecommunication Electric engineering Communication Electronics Science Technology
Publisher: [Short Hills, N.J., etc., American Telephone and Telegraph Co.]
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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Text Appearing Before Image:
the entire image field. The wave length of acomponent is A complete array of the components, up to m and n equal to 4, isillustrated in Fig. 4, As of course is characteristic of the harmonic analysis, the wavelengths and orientations of the components are seen to vary only withthe shape and size of the rectangular field, and to be independent ofthe particular subject in the field. A change of subject, or motion ofthe subject, merely alters the amplitudes of the components and shiftstheir phase; but their wave length and inclination with respect to theX-axis remain unchanged. Consequently, for the same rectangularfield all subjects appearing in it may be considered as built up from thesame set of components. For a still subject, the amplitudes and A THEORY OF SCANNING 471 phase angles of the cosine components, or the complex amplitudes ofthe exponential components, remain constant with time. For a mov-ing subject these complex amplitudes may be considered modulated asfunctions of time.

Text Appearing After Image:
-3 COMPONENT + 2, -1-3 COMPONENT 0,+2 COMPONENT +2,0 COMPONENT Fig. 3—Examples of field components. The real amplitudes amn for a circular area of uniform brightness on ablack background are relatively easily calculated, and this subject isalso a good one to study as a picture from some points of view because ithas a simple sharp border sloping in various directions. The amplitudes 472 BELL SYSTEM TECHNICAL JOURNAL for a circle of unit illumination of radius R are (9) where /i is the first order Bessel function. In this particular subjectall components of a given wave length have equal amplitudes; and the

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