the striding level is not less sensitive than 20" by which 5'' can be 

 estimated by quarter divisions It is important in straight line 

 work and in surveys where angles are being read between points 

 in widely separated horizontal planes. 



To Test the Side Adjustment, rock the striding level back 

 and forth over short arcs either side of the vertical. If it runs to 

 the right at one side and to the left at the other, it shows that the 

 vial lies diagonally across the line of the horizontal axis. The 

 i edification is identical with that of the "wind adjustment" in the 

 wye level which may be consulted on p. 8. A striding level should 

 at all times rest without strain or interference on its bearings. 

 This accounts for looseness of contact in this construction. To 

 prevent damage by wind or accident, however, a pin is provided in 

 one of the standards that engages an eye in the leg of the level 

 mount. 



To Test the Equality of Pivots, remove the telescope from 

 its bearings and replace it after the instrument has been reversed. 

 If the vertical axis is truly vertical and if the bubble has been ac- 

 curately adjusted to the V-notches and now shows a displacement, 

 the axles of the telescope may be suspected of inequalities. The 

 effects of even slight changes in temperature on the whole instru- 

 ment should be carefully considered and weighed in the evidence. 

 It is not so easy to keep a large theodolite in perfect equilibrium 

 even in apparently quiescent atmosphere. If the axle hubs are 

 actually shown to be in disparity by this test, the bubble will rise 

 toward the larger one and the matter should be either submitted to 

 the precise mechanic or double observations should be made in con- 

 formity with accredited practice. 



Applied to Mining or Tunnel Surveys, the striding level 

 cannot reasonably be expected to control the auxiliary telescope 

 whose inevitable errors must be corrected either by interchange- 

 ability or double reversed observations. Steep sights, of relatively 

 great vertical and short horizontal components, will magnify small 

 instrumental errors unless controlled by a striding level. For 

 straight line work with the main telescope, on inclined sights, a 

 properly adjusted striding level will therefore be conducive to the 

 best results; but for tunnel alignment, or other such work in the 

 plane of the instrument, double reversed sights, as in the collimation 

 test, is the infallible measure. 



The striding level that is mounted on two inside bearings on 

 the axle of the telescope is an expedient of very doubtful benefit. 

 If the inside bearings cannot be reconciled to the pivots on which 

 the telescope revolves, the idea must be regarded as a fallacy. 

 Theoretically the idea is just as absurd as the use of collars on 

 alidades (see p. 55). 



