Seven-feet Transit Instrument. 427 
the bars of the telescope are shown lengthwise, whilst 
those of the axis are perpendicular; in both figures the 
illuminator is shown, in one the polished surface, the back 
of the plate in the other ; in each it is seen under an angle 
of 45 0 , the elliptical perforation appearing as a circle. The 
removal of the inscription pieces having afforded the drafts- 
man but a limited view of the interior of the sphere, the 
parts are not represented with precision ; but nevertheless 
may serve well enough to elucidate the preceding description. 
In Plate XVII. fig. 6 , extending from the cones of the axis 
to those of the telescope, will be seen four tubes or braces, 
attached to the former about two inches from the pivots, and to 
the latter about ten inches from the centre piece ; these are so 
placed as to exert but a very slight pressure, and although 
deemed by Mr. Troughton essential in the Greenwich 
instrument, were considered unnecessary in mine, and for 
the diminution of expence, would have been omitted but for 
my interference ; in the Greenwich transit they were applied 
to counteract any disposition to flexure, when the instrument 
Was directed to the horizon ; and although the greater length 
of the Greenwich instrument, would render such an effect 
more likely to happen than in mine, still, as I had never 
heard the Astronomer Royal speak but in terms of the 
highest commendation of his instrument, I deemed it con- 
sistent with good sense to profit by his experience. 
Until the Greenwich transit was constructed, the method 
of placing the telescope to the required altitude, was by means 
of a semicircle fixed to one of the side pieces, and an index 
clamped to the pivot of the axis, the vernier of which pressed 
slightly upon the former. The index in this arrangement is 
