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43 6
being read in an exactly similar manner. It will be noticed tha . the specimen is stationary while the diamond is moved, thu. differing from the scler-ometer as applied to minerals ; the method of supporting the beam and of applying the weight is also different. In ordinary experiments, where considerable weights are applied, the diamond may be moved by the finger, and as the apparatus is very steady in its actions, with a little care this gives very concordant results. For more delicate observations with smaller weights, the diamond may be drawn by means of a horizontal string running over a small pulley. The surface used is prepared roughly in the ordinary way by chipping, filing, etc., and then with a smooth file; it is finished with emery paper, using at last the finest variety, or flour emery, and oil, according to the material.
A.    Beam.
B.    Knife-edge.
C.    Rotating1 Support. Steel Rod and Pivot. Diamond.
P.   Sliding Weight. G.   Adjusting Screw.
Sliding Weight.
Extra Weights. J.   Test Piece. K.   Wooden Support,
D. K.
FIG.    91.nt, bein.n1 obtained by the screw t). Wlien balanced, it is sensitive to o.oi gramme at 1C, though such delicaey is not probably required. Tin- knife edv;vs rest upon plain-s in tin* support (', whirls is eapahle of rotating on a steel pivot eon-iieeted with the rod I). The diamond is mounted in a brass tube, havin;..1,1 a milled head which is fixed by means of a screw at 1C. The specimen to be tested, which often takes the form shown, J, s-. supported by a wooden block K. The weight II is arranged r.o that each division on the j^radualetl scale shall eonvspoud to a pressure dj a gramme at the diamond point. Thus, at division r,, we have a pressure of 12 grammes on the diamond. Three estra weights, I, are used when necessary. Tlniy are each of the same weight as II. Uc-nee, with one weight, scale division m eorre:,ponds to m y^rammes on the diamond, with two weights i> corresponds to '/o grammes,with thr<*e weights to -\n ^nimmes, and \-ith tour weights to ,|o grammes, the other scale division:, in Volume XXIII. of the              .*