A pocket transit combining the useful features of a level, prismatic compass, and clinometer, is shown in the accompanying illustration. It was designed by W. D. Versehoyle, Esq., of London, England, a mining engineer who has wide experience in the use and application of various forms of instruments intended for preliminary surveys. The distinguishing feature of the instrument is that, ewing to its novel construction, only one observation is necessary to obtain both the magnetic bearing and the yertical angle of any distant point. It is also specially adapted for use in difficult positions such as are always liable to occur in filling in the rougher details in a mining survey. For rapid topographical work and working in con strained positions, it saves half of the labor. Another important point is that its efficiency is not determined by the length of the diameter of the compass, as is ordinarily the case. With even a small instrument the same length of sight is obtained as would be possible with a 6inch or 7-inch prismatic compass. The engineer can, himself, if necessary, make all the necessary adjustments. use the instrument for obtaining horizontal and vertical angles, after freeing the needle and unfolding the arm, the compass box is grasped in the left cand and with the extended fingers of the right hand the arm of the transit is lightly grasped, when the distant target or light is brought to the intersection of the cross lines at the end of the arm. When the arm is held firmly in that position the compass box should be slightly revolved until the bubble in the small level is seen to b'e at the central mark. The magnetic bearing will now be plainly visible in the prism at the same time that the target is viewed along the sight line and the angle of depression or elevation is automatically recorded on the vertical arc. Both readings can then be taken at the same time without further observation. A clinometer is an instrument used for taking the dip and strike of rock strata, In its commonest form it consists of a protractor with a pendulum attach(; When the clinometer lies horizontally the indicator pOints to 0 deg., and when inclined the amount of inclination is shown at once by the pendulum. In the instrument under consideration the clinometer and compass are combined in one instrument. When the device is used as a clinometer the bottom side of the arm is laid on the object to be observed and, looking through the window at the top of the compass box, the latter is slightly revolved until the small bubble comes to the center, when the angle may be read off the vertical arc. Should it be necessary to alter the relative position of the divided ring and the magnetic needle this can be done by removing the cover and altering the position of the needle immediately under the divided ring. Adjustment for magnetic variation may be obtained in this manner without disturbing the other adjustments. The pocket transit is designed as a serviceable instrument and is built to withstand the rough usage an instrument of this nature is liable to receive.
This article was originally published with the title "A Convenient Pocket Transit" in Scientific American 97, 18, 310 (November 1907)