Prof. E. V. Huntington, of Harvard, has published a book of 

 four place functional tables in which the sexagesimal degree is 

 divided decimally. * There is the same argument for using the 

 decimal degree as there is for the decimal foot. 



252015105 Y 510152025 



Fig. 58 shows the most likely method for the decimal subdivision 

 of a sexigesimal circle. The limb is divided into % or .25 spaces 

 exactly as in Fig. 56; but the vernier scale is constructed by sub- 

 dividing 24 such spaces into 25 equal parts so that the least count 

 will be M>5 of X r Hoo In reading this type of vernier it is 

 necessary to retain in the mind 25-, 50- or 75-hundredths of a 

 degree before seeking the addendum in the vernier scale. By 

 this method Ver. A. could be constructed as above and Ver. B. as in 

 Fig. 56 so that both the decimals of a degree, and minutes, could 

 be read on the same circle.** 



A Retrograde Vernier is one in which the numbering of 

 the scale increases in the opposite direction or one in which the 

 scales spaces are larger than those of the limb. Examples of retro- 

 grade verniers are given at A, C, and E, Fig. 54 showing three other 

 methods of producing a least count of 0.01. The verniers at E and 

 F are unusual. 



A Reciprocating or Folding Vernier partakes of the nature 

 of the direct and retrograde types, in that it may be read both 

 forward and backward. Two examples from our catalog Metro III 

 are reproduced herewith. The system and values are exactly alike 

 in each case but the smaller illustration, Fig. 59, shows the method of 

 nufnbering when only one zero point is permissible, as in reading 

 the quadrants of a vertical circle. 



Let it be supposed that a reading is to be taken downward or 

 toward the left. Start with the horizon at zero and follow along 

 the scale in the direction of 5 and 10. If no line is found in coinci- 

 dence, jump at once to 10 at the opposite end of the scale and continue 

 the count in the direction of 15 and 20. Where space is cramped 

 the same effect can be produced on small vertical circles, reading to 

 minutes, with a limb divided into ^ and an ordinary single vernier 

 of 30 spaces equal to 29 on the limb. 



* Harvard Co-op. Soc.. Cambridge, Mass. 1907, '08, '10. 

 **Sft also Railroad Field Manual, IV. C. Raymond. 79/5, p. L'.'. 



100 



