424 Description of Mr. South’s 
really merits the above reproach ; the investigation will be 
tedious, but I trust it will be satisfactory. 
The transit instrument employed for the purpose was made 
for me by Mr. Troughton ; its object-glass is four inches in 
clear aperture, its focal length seven feet two inches ; and as 
far as the just proportions of its parts are concerned, it is re- 
garded by him, as his happiest production. Experience having 
also shown that it is one which future artists will do well 
to imitate , a brief description of it will perhaps be grateful 
to the Society. 
The instrument in its general construction is similar to that 
of the ten feet transit, which was in the year 1816 erected at 
the Royal Observatory at Greenwich; there are however 
some trifling differences, which will be mentioned hereafter. 
In Plates XVI. and XVII. figures 1 and 6 , the instrument 
is shown on a scale of one-twelfth of the real dimensions. 
The telescope (as well as the axis), is formed of conical 
tubes, the extreme ends of which are determined by the 
diameter of the object-glass, whilst the larger ends take 
their dimensions from that of the spherical centre piece, which 
forms a base for them to rest on. In the two figures just 
referred to, the centre piece has nearly four-sixths of its sur- 
face covered by the four truncated cones of the axis and tele- 
scope ; but it is not rendered weak by the perforations made 
in it, those in the direction of the telescope being but a little 
more than the radius of the object-glass, whilst those in the 
direction of the axis are no larger than is required to transmit 
the light of a lamp placed near the end of the axis, unin- 
terruptedly to the central illuminator. The figures 1 and 6 
of Plates XVI. and XVII. do not at all show how the four 
