TRACT 35.

EPROUVETTE.

159

will probably be more convenient in several respects, as theshortness will render it easier to load and clean, as well asmore commodious in the act of vibrating ; besides, the actionof the fired gunpowder on it may be considered as only onesingle impulse, in which case the strength of the powder maybe considered as proportional to the velocity given to thepiece, and which therefore will be proportional to the chordof the angle of vibration, and may thus be measured and es-timated by it; and hence this one line of divisions only,viz, the line of chords, is all that may be necessary to bedrawn upon the limb of the arch.

10. To construct the line of Chords on the Arch.

The radius ef, of the arch to measure the vibration, it maybe convenient to make of about 12 inches in length ; andthe extent of the arch itself cd, about a quadrant or quarterof the circle. From the centre e, with the radius of 12 inc.suppose, scratch a. quadrantal arc, along the face cd of theinstrument, upon which arc the lengths of all the chords areto be laid down, the divisions of which will not be at equaldistances, or of equal lengths, after the manner of the equaldegrees on arches, but will continually decrease from thebeginning, where they are largest, all the way to the end,where they are smallest. Probably the best way of layingdown the divisions, will be as follows:

Take in the compasses the whole extent of the quadrantalarch, from the beginning at c, to the end at d, having mark-ed those two points, either by dots or short transverse lines.Lay that extent, which will be the chord of 90 degrees, upona straight line, drawn on some plate of metal, or other hardand smooth plane surface. Divide this right line into asmany equal parts, as the divisions of the intended chords onthe arch are intended to be, as for example 100 parts, whichwill probably be a convenient number, or sufficiently nume-rous. Then transfer these divisions, from the beginning ofthe line, to the arch, always from the beginning at c, to theextent that each may reach to along the arch, observing that