189 
Lieut. Foster’s account of the repetition , &c. 
a wooden frame, across the upper part of which passes a 
copper bolt, GH, with clamping screws at ss. This bolt 
was flattened and bent down in the middle, as shown at K, 
where the compass was placed. L M N O is a copper 
frame, with two pins, T and V, inserted into it, to carry 
the circular iron plate, as shown also in the figure. It is 
obvious, that with this instrument I was enabled to place 
the iron plate in any latitude by means of the graduated 
circle a a and plummet^, while by turning the frame C D E F 
in azimuth, it might, in like manner, be placed in any longi- 
tude : in all these cases the plane of the plate being a tangent 
to the sphere. When it was required to place the plate, with 
its edge pointing to the centre of the needle, or its plane in 
the plane of the secondary to the equator and meridian, I 
then employed the small stand shown in fig. 2, which might 
be elevated to any height to bring the compass, which was 
placed on its top, to the required position. It was also em- 
ployed when the plane of the plate coincided with that of the 
equator. 
In order to understand the particular positions in question, 
it will be best to refer to figures 3, 4 and 5. Fig. 3, repre- 
sents the sphere circumscribing the needle viewed on the 
plane of the meridian ; 4, on the plane of the secondary ; and 
5., on the plane of the equator. In fig. 3, C is the centre of 
the compass, SN the magnetic axis or line of the dip, E w O 
and e the equator, S E N Q the meridian, S^Nw the secon- 
dary, n w s e the horizon, ns the horizontal magnetic meri- 
dian or axis of the horizontal needle, and e cw the east and 
west line. The points at which Mr. Christie wished obser- 
vations to be made, were at E, S, Q, N, e and w, with the plane 
