106 : Mr. SAMUEL HUNTER, 
For a 2-feet speculum H K revolves about 132 times per 
minute ; the eccentric S I°7 times; V 347. The speculum A, 
0-46, T being 1°7 inches from its centre to centre of spindles, M , 
and V being 1:4 inches from centre of T. The curve described 
by the centre of the polisher in these conditions is shown in 
figure 7. An exactly similar curve would be obtained if S did 
not revolve at all (the revolutions of T being unaltered), and the 
speculum at a speed of 1°7+0°46, the sum of their velocities, 
equivalent to 1 turn of speculum to about 16 of V. The dotted 
line in figure 7 shows the path of the centre of T, the centre 
of the speculum being at C. It was found by Mr. Lassell that 
the polishing was apt to proceed in rings to the detriment of the 
figure, he caused the speculum to rest on a sliding bed instead of 
directly on the wheel C, which being acted on by a roller fastened 
to the wall plate, received a thrust of about one and a-half inches 
on two opposite sides. Delarue made a further improvement by 
causing the speculum slowly to revolve on this, so that the thrust 
did not always occur across the same diameter. 
Mr. Grubb’s First Machine. 

Fig. 8. 
This machine gives Lassell’s curves, and is capable also of 
approximating closely to Lord Rosse’s. 
fis a worm-shaft driving the wheel b of 90 teeth ; ¢ also of 90 
