L. 1C. Picolet in Eng. Nfivs, Apr. 1 ( >12, proposed a method <>i 

 separating double verniers, as shown in Fig. 57. In this system the 

 index line was made very prominent with a clear space of slightly 

 more than one degree at each side so that, while it performs the 

 function of the zero line common to both scales, the scales 

 themselves are separated, giving emphasis to the direction in which 

 the angle is to be read. 



13 10 5 u 10 15 



300 



no 



Fi*. 57 



The zero-lines of the separate scales, if they existed, would 

 occur at exactly one degree, or any desired number of integral 

 divisions to the right or left of the index line. The least count in 

 this vernier, as in Figs. 55 and 56, may be found by dividing the 

 smallest subdivision of the limb, 15', by the whole number of 

 divisions of either scale, 15, or 1'. As a rule, however, minute 

 graduations are not accomplished by any such fine subdivision of 

 the limb. /4 spaces on the limb and a vernier of 30 spaces equal to 

 29 on the limb, is the most legible form for minute graduations, t 

 Another method of obtaining the smallest count of 1' is to divide the 

 limb into ^ spaces and construct a vernier scale by dividing 19 

 such spaces into 20 equal parts. 



In 1801 Laplace suggested that the quadrant of the circle should 

 be divided into 100 degree-spaces (=^0 54' Sex. ) and that each of 

 these centesimal degrees, or grades, should be subdivided into 10 

 minutes, or 100 seconds; but the sexagesimal system already uimeis 

 ally adopted has not yet been widely replaced even though the 

 tremendous work of making the translation and compiling logarith- 

 mic tables has been accomplished. * 



Henry Briggs was the first to use the sexagesimal degree, 

 decimally. His Trig. Brit., edited by Gellibrand, was pub. 

 in 1633. This method has the great advantage of dispensing \\ith 

 both minutes and seconds without destroying the system itself. In 

 1856 M. Minot popularized it in France for laying off deflection 

 angles in railway curves, and S. \V. Mitflin used it with success in 

 the early construction of the Pa. R. R. 



t Ketrr also to Mines ami Minerals. 



* Til f>fes Trigonometry , 1889. 



