DJUSTMENTS of the transit instrument are 

 comparatively simple when the geometrical 

 elements and their relationship to one another 

 are fixed in mind. The vertical axis is a 

 vertical line passing through the spindle, 

 intercepted at the plates by a horizontal plane 

 and terminating in the line of collimation at 

 its intersection with the horizontal axis of 

 the telescope. This point in the telescope, 

 at the intersection of the horizontal axis, the 

 collimation axis, and the vertical axis pro- 

 longed, is the virtual center of the instrument. 



The Plate Bubbles are intended to establish verticality in the 

 compound centers and incidentally to level the plane of the graduated 

 plate. If these two functions are to be performed simultaneously, 

 it is evidently incumbent upon the manufacturer to build a vertical 

 axis that will remain permanently at right angles to the vernier 

 plates, and to construct journal bearings in the standards, moreover, 

 that can be secured at right angles to the vertical axis prolonged. 



The Azimuth Axis must also be built at right angles to the 

 plates or, in revolving the instrument, the vernier scales will appear 

 to rise and fall above and below the reading edge and cause parallax 

 of vision in consequence. 



The Sight Line and the axis of the telescope bubble must not 

 only be parallel but the construction must be such that the sight 

 line will revolve in a vertical plane, passing through the vertical 

 axis when focused for all distances in the field. 



When the Graduations are accurately spaced and perfectly 

 centered with respect to the azimuth axis and the other conditions 

 expressed above are fulfilled, then the instrument is, in the essen- 

 tials, qualified for reliable work; but the responsibility of the 

 manufacturer is so great in this accomplishment that he must share 

 with the surveyor to some extent the further accountability as to 

 the accuracy of the field work. 



The "Engineering Record" for Sept. 2, 1911 acknowledges 

 editorially that the amount of time and money wasted annually in 

 every city, in reaching compromises over boundaries of improperly 

 surveyed tracts, is very large. One of the steady incomes of the 

 legal profession is derived through the adjustment of failures on 

 the part of the surveyor. Errors of this kind arise from faulty 

 computations, careless procedure, or instrumental deficiencies which 

 the surveyor either does not recognize or correct. 



We have heard of young surveyors who were afraid to investi- 

 gate their instruments because they did not understand them, and 

 others who, having once set up an instrument, will not touch it 

 again at that station whatever the indicated errors. There are 



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