SURVEYING INSTRUMENTS. 347 



the horizontal limb is 7 inches in diameter, having on the 

 vernier plate two levels, and a 4-inch compass. The teles- 

 cope is fixed in the centre of the axis, and may be reversed 

 by turning one end over. A complete vertical circle, grad- 

 uated to half degrees, is on the axis of the telescope out- 

 side of its supports, with the vernier fixed to its branches, 

 and reading to single minutes. The vernier on the horizon- 

 tal plate is also divided to single minutes. The construc- 

 tion of the compass is the same as the last described. The 

 instrument is packed in a substantial mahogany box. 



Price $125.00. 



Price, without vertical circle, $120.00. 



" " " and level, $115.00. 



" " " " " and tangents, $100.00. 



Improved Transit Theodolite. (Fig. 785.) This in- 

 strument consists of two circular plates, the upper or ver- 

 nier plate A turning freely upon the lower, and both have 

 a horizontal motion by means of the vertical axis C. This 

 axis consists of two parts, external and internal, the for- 

 mer secured to the graduated limb, the latter to the ver- 

 nier plate. Their form is conical, nicely fitted and ground 

 into each other, and having an even and steady motion 

 when turned. The external centre also fits into the ball 

 at E, and the parts are held together at the lower end of 

 the internal axis. The diameter of the upper plate is 

 greater than the lower one, having also a rim covering 

 the outer edge of the lower plate. Near the edge of the 

 lower plate on its upper surface is the graduated circle, 

 numbered from to 360 degrees, and subdivided to half 

 degrees ; and on the same plane, and in close contact are 

 the two verniers, attached to the upper plate. These 

 verniers are placed on opposite sides, or 180 degrees 

 apart. They are divided from the centre each way into 

 thirty parts, numbered 0, 10, 20, 30 ; these thirty parts 

 correspond in extent to twenty-nine parts on the gradu- 

 ated circle, and consequently subdivide the same into sin- 

 gle minutes. The verniers and a portion of the graduated 

 circle are visible through openings in the upper plate, 

 covered by a light brass frame, and a closely-fitting glass, 

 in form corresponding to the arc of the circle. The par- 

 ticular use of this arrangement of the graduated circle 

 and verniers is that they may be protected from injury 



