The Portable Transit, for land surveyors and engineers, is ar 

 American invention dating back to 1831, when a low power tele- 

 scope was mounted, on plain truss standards over the dial of a sur- 

 veyor's compass to replace the sight vanes. This precedent has 

 dominated all subsequent practice and manufacture for, while 

 the vagaries of the compass are now well known, that feature is 

 still a conspicuous part of the modern instrument 



Our Transits are made in three sizes: the four, five and six-in. 

 models conforming closely to conventionalities except where, in 

 certain mechanical or optical details, we have been able to im- 

 prove the construction by adding to strength, accuracy or reliability. 



The Telescopes are provided with the objective draw tube 

 focus now in common use. The collimation is secured for all 

 distances without special adjusting screws or interior springs. The 

 focusing pinion, by common consent, is at the top; convenient 

 for either right or left hand, erect or inverted. 



The Standards are of symmetrical and unique design, being 

 reinforced at the base with a wide contact surface that permits 

 two dowel screws from beneath and one through the center from 

 the top. This is the most substantial system known to us. The 

 lateral stiffness is remarkable, (see also p. 130). 



The Vernier Reflectors are a special translucent milk glass 

 which not only reflects but transmits light for the ample illumin- 

 ation of the vernier plates. The vernier windows are flush with 

 the plate so that dust or rain can be readily removed. 



The Plate Bubbles are in the compass box protected against 

 accident and sudden temperature changes. They are mounted on 

 a swiveled base bar that offers unusually sensitive control and can 

 be adjusted by a capstan head screw from the outside. Removing 

 the plate bubbles from the zone outside the compass ring leaves more 

 room for vernier openings and contact surface for the standards. 



The Leveling Screws are provided with dust caps and dust 

 guards. The lower guard can be unscrewed and removed entirely 

 for mining work so as to insure a maximum tilt in the leveling 

 head. (See Fig. 123 p. 197.) 



The popularity of the 6-inch Transit has been sustained 

 mainly by those who have believed that the length of the needle 

 was a measure of its efficiency. We have received inquiries for 

 8-inch Transits with this conviction the evident purpose. 



The telescopic attainments possible with the 6-inch size, how- 

 ever, are plausible causes for preferment. In the matter of in- 

 creased stability, due to weight and the improved telescope quali- 

 fications, the 6-inch model stands pre-eminent among the portable 

 instruments. Stability does not necessarily increase with weight 

 because it is regulated somewhat by stiffness in the tripod head and 

 legs; but with the variable power eyepiece the magnification can 

 be increased to X27 without noticeably impairing the rectilinear, 

 planar or luminous qualities of the field. 



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