On Apparatus for Polishing Specula for Reflecting Telescopes. 101 
The polisher being now prepared the speculum was laid on it, 
being first gently warmed to about 80°, and moved about on the 
polisher gently until it was found that the pitch touched it at all 
points. Rouge and water was then applied and polishing com- 
menced, the operator proceeding as in grinding, carefully observing 
that the polishing proceeded equally. 
Tripoli was at first used, but is now entirely superseded by the 
sesquioxide of iron or Jewellers’ rouge, by which name it is sold 
in the shops. 
Mr. Mudge polished the speculum to a true spherical surface 
and then ended by a few large circular strokes upon the round 
polisher so as to increase the radius of curvature near the margin. 
I hope you will not consider that I have gone too much into 
detail, but as the machines used only change the mode of using 
the power, I shall not have to recur to these processes again. 
The disadvantages of hand polishing are, the unequal pressure, 
the inability to exactly control the length and direction of the 
stroke, theirregular increase oftemperaturefrom friction, and finally 
the inability to work specula larger than eight or nine inches in 
diameter. 
As already stated, Sir William Herschel was the first who used 
a machine in polishing, although it is not many years since a 
description of it was first published. 
We shall now proceed to describe it. 
Sir William Herschel’s Machine. 
The ring RS G surrounded the speculum which rested on the 
polisher face downwards; within this ring loosely fitting, and 
held in position by three pins above and below, there was a thin 
flat ring TK L,on which was screwed a ratchet ring; this 
annulus also carried three cocks at T, K, and L, which rest upon 
the speculum, with flanges projecting downwards, covered 
with felt, and capable of being adjusted go as to hold the speculum 
concentric, yet without being pinched; RC S is a claw attached 
to the ring by two pivots at R and §, and with an eye at C, to 
connect it by a pin to the lever A B, which pivots on B, the 
power being applied at A. D K and D L are two arms fastened 
i I 
