THE TACHYMETER 



ACHYMETERS and Theodolites of our design have 

 incorporated in their structure all the refinements of 

 manufacture known to the instrument maker's art. 

 The supreme technical skill of the artisan, as well as 

 the quality of the material and perfection of the 

 equipment, are the controlling factors in design and 

 production. Each instalment is sustained by the 

 conventional guarantee that covers the entire business 

 relationship of this house. 



The best materials only are employed. The inner center is 

 bell metal; the intermediate center, phosphor bronze; the outer 

 center, hard red composition and the leveling screws, German 

 silver. The standards are cast in one piece of aluminum bronze, 

 and the journals rotate on cylindrical bearings, of >4-in. diameter 

 and f'g-in. width, in morticed blocks of phosphor bronze. 



The Axis Bearings are true cylinders of equal diameter 

 universally acknowledged to be the ideal construction for any transit 

 instrument. Bearings that are recessed are weakened, and the scheme 

 multiplies the number of surfaces that are to be kept in nice relation- 

 ship for the important purpose of the horizontal axis adjustment. 



The recessed bearing is intended only to overcome side play in 

 the telescope journal, but we accomplish this bond by an entirely 

 different means which does not interrupt a continuous bearing sur- 

 face. The bearings of all transit instruments that are used in flat 

 country, where the telescope is tipped only a little above or below 

 the horizon, will sooner or later get a little worn on the under side. 

 The cylindrical axis bearing will unquestionably last the longest, 

 but it is always good practice to equalize wear by using the tele- 

 scope a part of the. time in an inverted position. In triangulation 

 this recourse is also necessary to correct for the eccentricities of a 

 colli mated telescope with respect to the center of the horizontal 

 circle, (seep. 129). A telescope that will not qualify as to collimation 

 adjustment for all distances is either mounted to one side of thecenter 

 or there exists an imperfect motion in the focusing slide. B. & L. 

 bearings are spaced equidistant from the center by a very accurate 

 mechanical process, after which the telescope is permanently fitted, 

 concentrically, without adjusting screws for the focusing tube, so 

 that the collimation test is satisfied for all distances. 



The Finish is a new weather-proof material in an olive 

 drab (khaki) tint which js very agreeable to the eyes in all climates. 

 This has superseded the cloth finish, which is used to cover a multi- 

 tude of sins and cannot be cleaned. 



The Vernier Windows are set, according to prevailing 

 custom, at about 30 off the direction of the sight line. This plan 

 makes the observation of Ver. A. a very convenient undertaking 



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