160

THE VIBRATING

TRACT 35,

every chord must commence at the point c ; viz, first lay offevery 10th division in the following manner: Take the ex-tent from the beginning of the line to the 10th division, andtransfer it to the arch, by placing one foot of the compasson the beginning at c, torn the other round to the arc thatwas described, with which make there a mark, for the 10thchord division. Next take with the compass the extent ofthe first 20 from the divided line, and transfer it to the arcfrom the beginning at c. In like manner transfer all theother extents of complete tens, viz, 30, 40, 50, 60, 70, 80,90, each extent from the beginning of the arc and of the di-vided line. In the same way transfer any of the intermediateseries from the divided line to the described arc, every ex-tent always commencing at the beginning of the line and arc,as the series 5, 15, 25, 35, &c, to 95. After the same man-ner let all the other intervals, from the beginning of the lineand arc, be transferred, as 2, 4, 6, 8, See, to complete thedivision of the arc to every 2 on the chords ; or the wholeseries 1, 2, 3, 4, Sec, to complete it to every single unit ofthe chords, if the space will allow of such minute divisions:iastlv, number the divisions at every 5, witli the numbers, 5,10, 15, 20, 25, &c, to 100, which will complete the arch tomeasure the velocit}: of the recoiling gun, and the strengthof the fired powder.

11 . Remarks and Directions for using the Eprouvelte.

This eprouvette, it may be remarked, is not confined toany one particular size, or even shape, as it may be either ashort cannon or a mortar, the latter probably the best; andthese may be either small or large. The present instrument,with a small cannon, is to be considered only as a model of.the cannon sort, to be used and charged with 2 or 3 ouncesof powder, and with which a multitude of experiments havebeen made, with perfect satisfaction; the results, even fromthis size, being remarkably regular. If it be desired to trylarge charges, then a larger mortar or gun may be employedin the same way; but the present small one is quite sufficiently