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MINUTES OF PKOCEEDINGS OF 
characters of the illumination are under complete control of the observer while 
actually observing. 
“ One other matter is perhaps worthy of note. 
“ The want of a convenient method of mapping nebulae or faint stars by a reti¬ 
culated diaphragm of bright lines in the field of view has long been felt, and the 
various methods of using diamond scratches on glass or illuminated lines are 
subject to objection, and troublesome to manage. A simple method of using an 
image of such a diaphragm instead of the actual diaphragm itself, here suggests 
itself. 
<c Referring to the portion of the rays used for bright field illumination, and 
shown in Fig. 1, suppose the small diagonal mirror, R\ to be replaced by an 
equally small prism having such a convex power that it forms an image of any 
object at the end of the declination axis exactly in the same plane as the image 
formed by the objective; then any kind of reticulated diaphragm of bright lines on 
dark ground can be placed on the end of the declination axis which would have a 
suitably prepared carrier for them, and their image would be seen in the field of 
the telescope of any colour and any intensity desired.” 
The right ascension circles are 8 ins. diameter, divided on palladium alloy to 
2 minutes of time; the lower circle fixed to polar axis, and read by opposite 
verniers to 2 seconds (time), and the upper (adjustable, and carried by clock) read 
for sidereal time by opposite fixed verniers, and differentially for actual right ascen¬ 
sions by eight verniers on lower circle. 
The declination circle is 15 ins. diameter, divided on 12-caret gold to 10' of 
arc, and read— 
(a) By rough setting reader from eye-end, 
(5) By opposite micrometer microscopes, subdividing divisions of arc to 
single seconds. 
The illumination is altogether supplied by one lamp, hanging on end of declination 
axis by a universal joint. 
This one lamp supplies illumination to the declination circle in three places, 
position circle in one, and the reflectors for illuminating the wires of micrometer in 
both dark and bright field illuminations. 
The clockwork is regulated by the most approved form of governor, and is 
supplied with means of altering its rate without stopping, also lunar wheels, to 
change motion of telescope instantaneously from sidereal to mean lunar. The 
clock drives telescope by a square-threaded screw ground into a sector of long 
radius, and cut most accurately according to the method of cutting teeth of sector 
of great Melbourne telescope (described in “ Philosophical Transactions ” by 
Rev* Dr. Robinson, F.R.S., and T. Grubb, F.R.S.) 
The framework of mounting is altogether of cast-iron to within 8 ft. of floor 
level; the framing being made in three parts, and having convenient arrangements 
for adjustment in latitude and meridian. 
The following nine operations are accessible to an observer while actually 
observing:— 
1 & 2. Clamping and slow motion in right ascension. The clamping by cords * 
the slow motion by either of three methods— 
(a) Hook’s joint handle from right ascension slow motion screw, which 
connects right ascension sector and clamp. 
