of Ingleborough above the Level of the Sea. 2.53 



ment through its axis, C is a radiated wheel with a solid 

 conical axis D*, on which revolves the hollow axis E of an- 

 other radiated wheel B. A is a circular graduated plate, of 

 which the hollow axis F is moveable about that of the wheel 

 B. The divisions have a radius of 5 J inches, and are read 

 off to 10" on two opposite verniers fixed to the wheel B. The 

 plate supports a pair of Ys TT, (placed on one side of the 

 axis,) in which rests an eighteen-inch telescope K, fitted up 

 with cylindrical collars LLf. The line of collimation lies 

 \\ inch above the plate, and about the same distance to the 

 left of the centre of the divisions. The plate A and wheel B 

 are both cut into teeth at the circumference, the former being 

 turned by the pinion G (fixed to B), and the latter by the 

 pinion H (fixed to C). The wheel B can be secured to that 

 of C by the clamp J, and the plate A to the wheel B by the 

 clamp I. The upper parallel plate N N, carrying two pair of 

 screws PP, fits to the inferior part of the axis D by means 

 of the hollow cone M. The lower plate O O is secured by its 

 socket R R to the same axis by screwing up the ball Q Q. 

 The screw S serves to fix the instrument to the head of a 

 tripod staff similar to the one drawn at page 8 of Mr.Simms's 

 Treatise J. 



The circle has only one telescope, and as the ground at 

 the stations where it was used proved impenetrably hard, it 

 was highly important that the staff should be set up immove- 

 ably firm. The (inflexible) legs being well extended, a flat 

 stone or flag, at least a foot square, and nearly six inches 

 thick, was laid under and in close contact with each leg. 

 Another flag, equally thick and broad but much longer, was 

 reared lengthwise against the outside of each leg, a little 

 above its contact with the under stone. Both flags should be 

 quite firm, and front the centre of the circle on which the legs 

 stand. The figure in the margin 

 is a vertical section of the two 

 flags and leg through the points 

 of contact. Perfectly successful as 

 is the method, without regard to 

 the force of the wind, on massive 

 rock, it was generally found to 

 fail when attempted on any less 

 solid basis. At Clougha, the instrument being well set up on 



• The parts constructed of bell-metal are shaded in the figure. 



t In the plate the telescope and Ys arc given in elevation. 



X The circle was made to order by the late Mr. Allan, and cost about 30/. 



