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Durand, Loyal, Jr. (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XXXI (1938)

James, Harry Raymond; Birge, Edward A.
A laboratory study of the absorption of light by lake waters,   pp. [1]-154 PDF (46.6 MB)

Page 15

 In designing the apparatus provision was made for handling large quantities
of radiant energy and for a sensitive and steady means of measuring energies.
 The optical system consists of a monochromator of special size with attendant
external lens system for forming a parallel beam of light, to be passed through
the water to be tested, and focused on the slit of a monochromator. After
dispersion in the monochromator the light energies are measured by means
of a thermopile and galvanometer. Two different sources of light are used;
a tungsten strip filament gas-filled lamp, designed especially for spectroscopic
work, supplies the energy for the spectral region from 8000 A to about 4500
A; and a quartz mercury arc lamp is used in the region from 3650 A to 5460
A. The two ranges thus overlap enough to give a close check on the relative
behavior of the two sources. Fig. 1 shows a perspective drawing of the arrangement
of the optical system, together with the tubes for holding the water to be
tested and the comparison cell; all as used for the work on distilled water.
Fig. 2 shows the plan of the apparatus. 
Fig. 1 shows the monochromator, lens mountings, and specimen tube supports,
all carried upon a 6-inch steel channel beam 4.2 meters long, to hold all
parts in correct relation to each other when adjustments are made. In this
figure the galvanometer and scale, thermopile, light sources, monochromator
cover, shutters and screens for guarding against stray radiation, are all
removed for clearness in showing the basic system. The tube mounts are attached
to an iron pipe 5 cm. in diameter; the pipe is mounted upon adjustable pivot
bearings at each end and the center is supported by a straight bearing to
increase the stiffness of the movable system. Two of the tube supports are
fitted with curved iron arms which extend around and under the edge of the
table, and hold weights to counterbalance the weight of the tubes and contents
so that they are in neutral equilibrium in all positions of their swing in
and out of the beam of light. This ar15 

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