SIS

NEW EXPERIMENTS

TRACT 34*.

were at first placed to turn upon smooth flat plate-ironsurfaces, having perpendicular pins put in before and be-hind the sides of the axis, to keep it in its place, and pre-vent it from slipping backwards and forwards. But, thismethod being attended with too much friction, the ends of theaxis were afterwards supported and made to roll upon curvedpieces, having the convexity upwards, and the pins, beforeand behind the axis, set so as not quite to touch it; whichleit a small degree of play to the axis, and made the frictionless than before. But, still further to diminish the friction,the lower side of the ends of the axis was narrowed off alittle, something like the axis of a scale beam, and made toturn in hollow grooves, which were rounded down at bothends, and standing higher in the middle, like the curvatureof a bpnt cylinder; by which means the edge of the axistouched the grooves, not in a line, but in one point only;and then it vibrated with very great freedom, having onlyan almost imperceptible degree of friction. The severaltimes and occasions when these, and other improvements,were introduced and used, are more particularly noticed inthe journal of the experiments.

15. At first, the chord of the arc, of vibration and recoil,was measured by means of a prepared narrow tape, dividedinto inches and tenths, as before. A new’ contrivance ofmachinery was however made for it. From the bottomof the pendulum, or gun-frame, proceeded a tongue ofiron, which was raised or lowered by means of a screw at b ;this was cloven at the bottom c, to receive the end of thetape, and the lips then pinched together by a screw, whichheld the tape fast. Immediately below this the tape waspassed between two slips of iron, which could be broughtto any degree of approach by two screws ; these pieces weremade, to slide vertically up and down a groove in a heavyblock of wood, and fixed at any height by a screw d. Oneof these latter pieces was extended out a considerable length,to prevent the tape from getting over its ends, and en-tangling in the returns of the vibrations. The extent of