Engineers' surveying instruments, their construction, and use by Baker Ira Osborn 1853-

Author:Baker, Ira Osborn, 1853-
Language: eng
Format: epub, pdf
Tags: Surveying
Publisher: New York, Engineering news publishing co.
Published: 1888-03-25T05:00:00+00:00

.54

THE STADIA.

be varied at will. Lines are made upon the slides b and c to assist in placing the hairs parallel to each other.

The objections to this construction are, first, that it is expensive; second, that the projecting heads of the adjusting screws are liable to be struck and turned in handling the instrument or in carrying it through brush, and so produce a serious error with no adequate means of detecting it; and third, since a spring must be inserted to take up lost motion, the screws have a tendency to work loose.

4. Fig. 2, shows a much better way of making the hairs adjustable ; a, b, c, and d are small wire plugs which are free to turn, being held only by friction; the shaded portion is in the plane of the face of the ring, the unshaded portion projects, say i of an inch above. The crosshairs are to be stretched in the line of the centers of a and d, and cand b, and fastened at the outer edge of the ring; then, by turning the plugs, the hairs will be moved toward or from the central one, according to which side of the-plug is toward the center hair. The wires may easily be made to fit

tight enough not to work loose, and still turn freely enough for the

above adjustment.

With telescopes having inverting eye-pieces, which are much the best for stadia work, the wires can be turned by removing the eye-piece and without taking the reticule out of the telescope tube. "With an erecting eye-piece, the hairs can be adjusted without removing the ring from the telescope tube, by making a little wrench (by cutting a kerf with a hacksaw in the end of a small strip of brass) especially for the purpose, and operating it through a hole in the telescope tube, also made for the purpose and which can be closed by a band; or the ring may be removed from the tube to adjust the stadia hairs. The telescope does not need to be collimated to test the relative position of the stadia hairs.

This method provides a way of making the hairs parallel to each other, and allows a variation in the distance between the cen-

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