432.—For tunnelling underground railways the mining theodolite described further on will be found the most valuable for railway engineers.
433.—Mountain Transit Theodolite.—This instrument, Fig. 181, is designed for geographical exploration, and making sketch surveys. It embraces the transit principle for the convenience of taking zenith stars. It is made in 3-inch and 4-inch sizes. It has two verniers to the horizontal limb reading to minutes, and a single vernier to the vertical circle. It has been made by the author in aluminium alloy only, the total weight being 2¼ lbs. for the 3-inch and 3½ lbs. for the 4-inch. The eye-piece reads direct or diagonally. It has clamp and tangent adjustment to both circles, and a trough compass. The tripod slides up to half length, each leg being adjustable to fix to any length within the range of the slide to accommodate it to the surface of inclined rocks.
434.—A Mountain Theodolite is a term applied to any very small or light theodolite. These are generally made to order, very frequently to a reduced model of a larger theodolite, 3 inches being a common size. The telescope is occasionally placed upon the side of the horizontal axis to transit. Theodolites of this class generally weigh much more than the above-described instrument, a common weight being 5 to 7 lbs.
Fig. 181.—Stanley's mountain transit theodolite.
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435.—Improved Solar Attachment.—The reviser's improved solar attachment admits of a full vertical circle being employed; it also has a clamp and tangent to the hour circle and declination arc and quick acting clamp and fine adjustment to the solar arm. An instrument so fitted is shown on p. 260, Fig. 182.
Fig. 182.—Stanley's solar attachment.
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