332 SURVEY OF THE COAST 



which projects a little more than an inch beyond the column, 

 to bear the supports of the transit axis of the telescope. 



The axis of the transit is nine inches lon^. Its two parts, 

 as well as the two parts of the telescope itself, are screwed 

 in a spheric centre piece of about two inches and a half in 

 diameter, and are in all respects similar in construction to 

 the telescope of the two-feet theodolite. The telescope it- 

 self is nineteen inches long and of two inches and a half aper- 

 ture. It has a lengthening or rather sheltering tube before 

 the object glass, and in the focus three vertical and three ho- 

 rizontal threads of cobweb. The eye glasses are exactly the 

 same as those of the two-feet theodolite and repeating cir- 

 cles; so that they will serve for any of these instruments 

 in case of loss. The largest magnifying power is about for- 

 ty-five times. 



On the side of the telescope tube opposite to the circle, 

 there are two small pins or axes, which are adjustable, and, 

 by receiving a level constructed for the purpose, make this 

 telescope serve as a very fine levelling instrument. 



Through one side of the axis the wires in the focus are 

 illuminated by the lantern which is placed upon a light pro- 

 jecting piece opposite to the axis, and fastened to the piece y 

 by a screw. 



The other part of the axis of the telescope forms the axis 

 of the vertical circle, which revolves upon it in a manner 

 exactly similar to that of the horizontal circle upon its axis. 



An alhidade, bearing two diametrically opposite verniers 

 W, X, is fastened to the axis of the telescope by its middle 

 circular part, and forms the outer reading upon the divisions, 

 exactly as in the horizontal circle, and clamps in like manner 

 to the outer part of the limb. 



A triangular piece, of which one side is horizontal, iiears 

 the two diametrically opposite readings Y, Z, reacliing upon 

 the division from the inside, and clamping to the limb of the 

 circle by means of the inner recess between its plane and the 

 plane of the radii. 



