430 
Description of Mr. South’s 
that the screws might be both moved at the same time, by 
equal quantities, and when the observer’s eye is at the 
telescope, there is a system of pinion work, the handle for 
which adjustment is seen in Plate XVII. fig. 6 , hanging down 
close to the inside of the western pier. In the formation of 
the side plates very great attention was paid to render them 
steady in themselves, as also that their respective adjustments 
should not disturb each other.* 
Fig. 5. Plate XVI. is a bird’s-eye view of the head of one of 
the piers, and was meant chiefly to show the apparatus for re- 
lieving the pivots of the axis, and Y*, from a great part of the 
weight which would otherwise bear upon them. Immediately 
behind the adjustable Y piece, but rather broader, is a plain 
piece of brass, having a Y cut in its upper end ; a lever also 
is seen, one extremity of which passes into a hole made in 
the Y piece just alluded to, whilst the other end carries a 
weight ; the bar of the lever is expanded into a circle, whose 
centre is about one-third of the lever’s length distant from 
the pivot of the axis. The circle is sufficiently large to admit 
the illuminating lantern ; in its diameter at right angles to 
the direction of the lever are inserted two steel screws, whose 
blunted points are hardened and polished; these rest on 
hardened and polished steel planes, which are let into the 
stone pier, and together form the fulcrum in a manner not 
• How completely this desideratum has been attained, it is only necessary to 
remark, that on the 9th of May, 1822, the western side plate was removed from its 
pier, in order that Mr. Troughton might apply to it, the pinion work just alluded 
to; on the 19th of the same month it was returned to me; and although not even 
an approximate meridian mark was at my command, still, by one observation of 
the pole star on the same evening, the instrument was placed so nearly in the plane 
of the meridian, that by the subsequent transits of Arcturus and a Libras, its ex- 
meridian position could not be detected. 
