26 



A MANUAL OF TOPOGRAPHIC METHODS. 



The value of a division of the level is commonly measured with a level 

 triei - . The latitude level may, however, be easily measured by means of 

 the micrometer, the value of a revolution of that being obtained by the fol- 

 lowing method: 



Point the telescope upon some well-defined terrestrial mark and set 

 the level at an extreme reading near one end of the tube. Set the movable 

 thread upon the object and read the micrometer and the level. 



Now move the telescope and level, until the bubble is near the other 

 end of the tube. Again set the movable thread upon the object and again 

 read both micrometer and level. It is evident that the micrometer and the 

 level have measured the same angle, and that the ratio between these read- 

 ings equals that between a revolution of the micrometer and a level division. 



An example illustrative of this is appended. 



Determination of ratne of 1 division of latitude level No. 534. 

 [ By comparison with micrometer screw 534 ] 



log 16095. = 4.20669. 



A. C. log 9241.9 = 6.03424. 



log 1 Div. Micrometer == 9.87966. 



1 Div. level =1".320 log. =0.12059. 



