8‘J2 MR. A. E. TUTTON ON AN INSTRUMENT FOR GRINDING SECTION- 
(j, provided with milled head. The screw passes through an arm radiating from the 
collar, and presses a small fidction brake against the flange of the cone c. The collar 
similarly tails off into an arm upon the other side of the centre; and this arm, to¬ 
gether with the collar, the cone c (when tixed to the latter), and all that moves with 
it, is capable of being slowly moved by means of a fine adjusting screw /?, provided with 
milled head. The arm is always pressed against the end of the screw by a piston 
actuated by a strong spring confined in a cylinder closed at one end. The long 
cylindrical nut of the screw, and the cylinder containing the spring and piston, are 
arranged on opposite sides of the arm in the same straight line, and both are fixed to 
the cross-plate a. E-otation of the milled head in either direction consequently 
produces slow motion of the collar and circle, and all that moves with them. 
The angle of the conical bore of the fixed cone fi, and of the exterior of c, is but 
slight, and the bore of c is made truly cylindrical. Within this cylindrical socket 
slides an axis i of gun-metal, independent rotatory motion being prevented by 
grooving it longitudinally and fixing a corresponding metal rib upon the interior 
surface of c. Hence this axis always rotates with the circle, but is capable of free 
upward and downward motion. It is held in position at a convenient height by 
means of a pair of levers h, heavily weighted at the ends of the power arms; their 
fulcrum supports I are fixed upon the circle-plate, and their shorter curved arms 
press upwards against a split collar m, which is fixed to the axis by means of a 
square-headed tightening screw worked by a key. The counterpoises n are so 
adjusted that when the lever arms are approximately horizontal the whole weight of 
the axis i and all that it carries is nicely balanced, and the slightest touch of the 
levers is sufiicient to cause up or down movement of the axis. The function of the 
axis i and the counterbalancing arrangement is to enable the pressure with which 
the crystal bears upon the grinding disc to be modified according to the strength of 
the crystal, and the mode of using it will be hereafter described. 
It is found convenient to have an adjustable screw o, resembling an electrical binding 
screw in shape, wuthout the lateral holes, slightly to the outside of the fulcrum of one 
of the levers ; the cylindrical nut in which the screw works is fixed to the circle-plate 
right under the long arm of the lever, so that the head of the screw may be made to 
support it at any convenient height. This lever is thus capable of free motion in the 
direction in which the counterpoise goes upwards, but it is prevented from moving in 
the opposite direction. The other lever is not so restricted, but it is prevented from 
moving so that its weighted ainn becomes inconveniently depressed, by means of a fixed 
elbow ^ 0 . The ease with which the axis i slides in its socket may be modified by 
aiiotlier split collar q, which encircles a flange (also split) standing up from the circle- 
plate and binds it more or less tightly to tlie axis according to the manner in which 
the square-headed tightening screw is arranged. The collar is made to loosen readily, 
upon retrocession of the screw, by connecting the two projecting ends through which 
the screw |)asses by a strong spring bent closely u])on itself. 
