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The universal transit designed by the reviser is shown at Fig. 187.
This is an 8-inch instrument, reading by micrometers on both circles to 2 seconds of arc, and is fitted with all the necessary arrangements for universal work.
A description of the larger geodetic instruments is given in a subsequent chapter.
CHAPTER IX.
PLAIN THEODOLITES IN WHICH THE TRANSIT PRINCIPLE IS NOT EMPLOYED—THE PLAIN THEODOLITE—IMPROVED CONSTRUCTION—EVEREST'S—SIMPLE—ADJUSTMENTS AND EXAMINATION OF THEODOLITES.
437.—The plain theodolite is of nearly its original form as invented by Sisson. It still retains a limited popularity, which is principally due to its portability, being of less bulk and weight than the transit of equal diameter of circle. If we consider the railway theodolite described in the last chapter as a simple form of transit, this must be considered as an exception with regard to the bulk and weight, not being greater than that of the plain theodolite.
438.—The Plain Theodolite.—For the general description we may follow that given in Chapter VII. for the 6-inch transit for all parts of the instrument below the vernier plate, and for the compass-box above this plate. The construction of the instrument varies from the transit in having a half vertical circle only, with a single vernier, and in the differences in the arrangement of the fittings connected with the telescope. A single microscope is generally used on the horizontal circle, and this passes in a groove from one vernier to another, instead of having two microscopes on arms jointed upon the vertical axis, as in the better construction of transits before described.