either single or double, depending upon 

 whether the limb is supplied with one or 

 two rows of figures. If angles were al- 

 ways read from left to right, there would 

 exist the necessity for only one row of 

 figures and a single vernier by which 

 the possibility of error in reading would 

 be nearly, if not quite, overcome. 



Examples of direct verniers, each 

 having a least count of 0.01, are given at 

 B, D, and F in Fig. 54 which is repro- 

 duced from an article by G. H. Bain- 

 bridge Jr. in Eng. News, Jan. 25, 1912. 

 Other examples of direct verniers as ap- 

 plied to transits are shown in Figs. 55 

 and 59. 



350 



Fig. 55 shows a single vernier, read- 

 ing to minutes, applied to a circle with 

 one row of figures reading clockwise 

 consecutively from to 360. This 

 method of numbering is most popular 

 for mining theodolites. With extra 

 heavy and legible lines the difficulties 

 ordinarily attendant upon that class of 

 work are leduced to a minimum. 



Fi*. 54 



190 



VO 180 



Fig. 56 



Fig. 56 shows a double vernier of the same construction with 

 a scale running each way from a central zero point or index line 

 There being two complete verniers in this scale, there are always 

 two lines in coincidence, which adds something to confusion and 

 the consequent possibility to error. 



