File:The railroad and engineering journal (1887) (14735303156).jpg

Identifier: railroadengineer62newy (find matches)
Title: The railroad and engineering journal
Year: 1887 (1880s)
Authors:
Subjects: Railroad engineering Engineering Railroads
Publisher: New York : M.N. Forney
Contributing Library: Carnegie Library of Pittsburgh
Digitizing Sponsor: Lyrasis Members and Sloan Foundation

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nakedeye down to .001 ft., and with much more exactness thanif the original scale had been actually divided into thou-sandths of feet. The vernier was invented in 1861, and takes its namefrom the name of the inventor. Plate XVIII represents the two plates of a transit, thevernier scales .4 and ^diametrically opposite each other.These verniers can be divided in a number of ways, and Vol. LXII, No. 2.) ENGINEERING JOURNAL. 57 the most common way is as follows : The outside circle isdivided into degrees and half degrees. Tal<e 30 of thesesmallest divisions on the outside circle and make thevernier equal 29 of them, and divide it into 30 parts ; weare thus able to read to minutes in angular measure. vernier are made equal to 39 spaces on the circle. In thesame manner the most minute divisions of angular measure-ment can be read. Of course the only limit to this is thelength of the diameter of the circle, because as the divis-ions become finer and finer, on an ordinary transit they be-
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Where more exactness is required the circle is dividedinto degrees and thirds of a degree (20 minutes). Then20 spaces on the vernier are equal to 19 spaces on thecircle, which reads to minutes, or if it is required to readJhe half minutes or 30 seconds, then 40 spaces on the come too fine for accuracy and increase the cost, so thatthey seldom read to less than 30 seconds. The transit, when it is lo be used for stadia measurements,frequently has a vernier divided on the decimal system, sothat any reading of angular measurements is taken in de- 58 THE RAILROAD AND (February, i88S. grees or decimals of degrees. The advantage of this, inthe case of stadia measurements, is that under ordinarycircumstances all the angular measurements are takenfrom the azimuth to the right, the same as the hands of awatch, through the whole 360 degrees of the circle, and innotes taken in stadia work there is much addition and sub-traction to be done. ft facilitates the calculations verymuch if the readings

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