350 Mr. Christie on the magnetism of 
revolve about the axis S 5 n N, while S Q N is fixed. S JE'bi 
and S Q N are graduated from JE and Q towards S and N, as 
is likewise s an from a towards s and n. The semicircle 
S Q N passes freely through an opening in the support G I, 
but may be clamped firmly in any position by means of two 
strong screws, working into the parts G,GTrom the back of 
the instrument. On the chamfered edge of the opening g, in 
the face of G G, is an index showing the inclination of the 
axis S N to the horizon ; and on the part Kk at the foot of 
the pillar, and attached to it, is an index pointing out on the 
graduated circle L /, fixed on the table T t, the situation of 
the fixed limb S Q N with respect to the magnetic meridian. 
R r is another graduated circle, fixed to the moveable limb 
S N ; which, by the index at x on the fixed limb S ^ N, 
shows the angle described by S N from the plane of S Q N. 
A very strong brass pin, soldered to the foot of the pillar, 
passes through the table T t and a thick circle of wood, to 
which the legs are attached, and has below a clamping screw, 
to fix the whole firmly together in any position. The com- 
pass box N' S' is fitted on to a stand fixed to the support F/, 
which consists of two parts ; f fitted to G, and F sliding on 
a tube attached to/; so that the compass may be elevated 
or depressed. An arm A B, to carry the circular plate of 
iron C r, is connected with the moveable limb S ^ N. The 
part A a consists of two flat pieces, having the limb of the 
instrument between them, so that the arm may be moved 
into any position on it, and be fixed in that situation by means 
of a strong screw working into the face A a. On the cylin- 
drical part B 6, a short hollow cylinder slides freely, having 
a circular rim raised .6 inch from it, to support the iron plate 
