Lord Webb Seymour on a Clinometer. 387 



spirit level EE, and the compass oo o. This axis is made to move 

 with a degree of friction sufficient to support the weight of the 

 radial bar in any position. The level turns upon its axis by two 

 pivots p p set in two small plates projecting from the extremities 

 of the radial bar, and through the same plates, immediately below 

 the level, passes a strong conical axis rr^ to one end of which 

 the compass is fixed, and with which it revolves. 



The compass-box has its bottom, as well as its top, made of 

 plate-glass, and each of the two pieces is set in a cylindrical rim of 

 brass which forms its sides. To the middle of this rim there is fixed, 

 on the inside, an annular brass plate, silvered and graduated in 

 the same manner both above and below. The divisions are of 

 two degrees. There are two zeros, one in each intersection of a 

 line passing through the center, and on both sides of each of them 

 the divisions are numbered alike, till they meet in two nineties, in 

 a line at right angles to the first. At ^ is a catch for working a 

 bolt sliding on the outside, which lifts the needle from its pivot in 

 the usual way, by the bent lever j-. The needle has the north 

 pole marked on the under, as well as the upper, side, and also an 

 index line drawn from one end to the other. 



In adjusting .the different parts of the quadrant to each other 

 regard must be paid to the following circumstances ; that the axis 

 of the level may be parallel to the line from the center of the 

 quadrantal arch to the index on the radial bar ; again, that when 

 the radial bar is home upon the base, the axis of the level may be 

 parallel to a line, in the plane of the base, from the center to the 

 index of the base, and that the index of the radial bar may at the 

 same time point to zero ; also that the fine of the two zeros in the 

 compass may be parallel to the axis of the level, at least, when the 

 plane of the compass is at right angles to that of the quadrantal arch. 



3 c 2 



