Artillery Circular Volume 3 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1893 Excerpt: ...accurate reading than that given by the nearest line of the vernier may often be made by subdividing the vernier division by the eye. Vernier Of Azimuth Circle. Fid. 39. On the azimuth circle the circumference of the limb is graduated to degrees and degrees and the graduations are numbered, for convenience, both ways from 0 to 360, as shown in the figure; the vernier is then doubled so that the fraction of the limb division on either side of the o of the vernier may be measured by using the graduations on the other side. Twentynine degrees on the limb are taken as the length of each side of the double vernier and this length is divided into 30 equal parts. The least count is therefore .6 of a degree, or i'. In measuring an angle with the azimuth circle, the reading on the limb and on the vernier are always given by numbers which increase in the direction the vernier is moved. Thus: if the vernier is moved from left to right, the numbers which give the readings increase from left to right; if the vernier is moved from right to left, the numbers which give the readings also increase from right to left. If the vernier, in the above figure, was moved from left to right to its position, the reading on the limb is 330; the raiding on the vernier, 19'; the true reading, 330 19'. if from right to left, the reading on the limb is 29 30'; the reading on the vernier, 11'; the true reading, 29 41'. If the graduations are accurate and the readings correct, the sum of two such true readings will always equal 360. Use Of The Azimuth Circle. Before either the azimuth circle or the transit can be used it must be in adjustment. An instrument is in adjustment when its different parts are in their proper relative positions so that work done with it will be ...