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"No part of the equatorial mounting is shown in the figure, as it resembles every respect that usual Fraunhofer mounting. An adapted h is fixed on a telescope-tube, made of wood, in Fraunhofer's usual fashion. To this adapter is attached a flat circular flange h. The slides carrying the segments of the divided object-glass are mounted on a plate, which is fitted and ground to rotate smoothly on the flange h. Rotation is communicated by a pinion, turned by the handle c, which works in teeth cut on the edge of the flange h. The counterpoise w balances the head about its axis of rotation. The slides are moved by the screws a and b the divided heads of which serve to measure the separation of the segments. These screws are turned from the eye-end by bevelled wheels and pinions, the latter connected with the handles a', b'." —The Encyclopedia Britannica, 1903

Heliometer

"No part of the equatorial mounting is shown in the figure, as it resembles every respect that usual…

"The original Merz micrometer of the Cape Observatory, made on Fraunhofer's model. S is the head of the micrometer screw proper, s that of the screw moving the slide to which the so-called "fixed web" is attached, s' that of a screw which moves the eye-piece E. C is the clamp and M the slow motion in position angle, L, L are tubes attached to a larger tube N; the latter fits loosely on a strong hollow cylinder which terminates in the screw V. By this screw the whole apparatus is attached to the telescope." —The Encyclopedia Britannica, 1903

Micrometer

"The original Merz micrometer of the Cape Observatory, made on Fraunhofer's model. S is the head of…

"A spectrum of sunlight is crossed by dark lines, many hundreds of whcih have been counted and accurately mapped. The more conspicious of these dark lines are distinguisged by letters of the alphabet. A few of these dark lines in the solar spectrum are due to absorption in the earth's atmosphere, but by far the greater number originate in the selective absorption of the solar atmosphere itself." — Avery, 1895

Visible spectrum

"A spectrum of sunlight is crossed by dark lines, many hundreds of whcih have been counted and accurately…