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865.—Dome Spectacles—Bogles.—Spectacles of neutral tint are most comfortable for general wear in sunny or snowy countries. The dome or globular form is generally preferred. Where there is hot dust gauze sides are to be preferred. There is a very cheap form with gauze sides, which holds on the head by an elastic band, termed bogles. These are rather hot to the face, and the band after a time becomes sticky. The spectacle form is much better. The glasses are made in various shades to choice: some very dark or even black, the latter being made for viewing and tending arc lights.
866.—Whistles made very powerful are much used in exploring abroad to bring the party together, and for signalling generally by sound, using the Morse signals, [art. 803].
867.—Pioneers' Tools.—A small set of these is often very useful to the surveyor in new forest countries. The common set consists of a claw-hammer, wood-chisel, stone-chisel, pincers, screw-driver, gimlet, and brad-awl. The leather case is 8 by 4 by 2½ inches; it weighs 1¾ lbs. with strap. This may be supplemented by a small American saw, cutting both edges, about 20 inches long, and the axe previously described, with a few pounds of wire nails. The tools serve for marking trees or rocks, erecting signals, temporary covers, etc.
868.—Sketch Block Book—Pocket Book.—In reconnoitring no better information can be given of a track than forward sketches from commanding station to station. Sketch books about 7 inches by 5 inches are generally found sufficient. The drawing-paper should be thin, and the pocket large enough to contain all the separate sheets as they are taken off by the penknife after completion from the block. The sketches may be made with pencil, or a fine fountain pen; or if the surveyor be a colourist a light box of moist colours and a water bottle will often leave pleasing sketches as reminiscences. Pocket-books with section lines to 1/8 inch or 1/10 inch scale are sometimes used to give approximate plans to scale of buildings, etc., where required, as well as the ordinary field-book record.
869.—Camera.—Recently the camera has been much used for reconnoitring. These are now made very light and portable to take ¼ plate or 3 × 3 inch films, either on rollers or in separate films.
870.—Cement Testers are made in various manners, generally to test the cohesion of the cement as a homogeneous hard body. Mr. Mann's cement tester, Fig. 421, goes on another principle—it tests the adhesion of the cement to stone, which appears to the author to be its most important function; it is always hard enough.
Fig. 421.—Mann's cement tester.