(440)
long Wine-staple B in the Ball A, and a springing wire C, with a bended end F, and into the said Staple, press in with your fingers the springing Wire on the bended end: and on it hang the weight D, by its hook E, and so let Globe and all sink gently into the water, in the posture represented in the said Figure, to the bottom, where the weight D touching first, is thereby stopt; but the Ball, being by the Impetus it acquired in descending, carried downwards a little after the weight is stopt, suffers the springing Wire to fly back, and thereby sets it self at liberty to re-ascend. And by observing the time of the Ball's stay under water (which may be done by a Watch, having Minutes and Seconds; or by a good Minute-Glass; or best of all, by a Pendulum, vibrating Seconds; the which must be three foot, three inches, and one fifth of an inch long, viz. between the middle of the Bullet and the upper end of the Thread, where it is fastned, or held when it vibrates.) You may by this way, with the help of some Tables, come to know any depth of the Sea.
Note, That care must be had of proportioning the weight and shape of the Lead, to the bulk, weight, and figure of the Globe, after such a manner, as upon experience shall be found most convenient.
In some of the Trials already made 'with this Instrument, the Globe being of Maple-wood, well covered with Pitch, to hinder soaking in, was 5 inches in Diameter, and weighed 2½ pounds; the Lead, of 4½ pounds weight, was of a Conical (but is now used of a Globous) Figure 11 inches long, with the sharper end downwards, 1 at the bottom in Diameter. And, in those Experiments made in the Thames, in the depth of 19 foot water, there passed between the Immersion and Emersion of the Globe, 6 Seconds of an hour; and in the depth of 10 foot water, there passed 3½, Seconds, or thereabouts: From many of which kind of Experiments, it will likely not be hard to find out a method to calculate, what depth is to be concluded from any time of the like Globes stay under water: As for instance, if in the depth of 20 fathom, measured by the Line, the Globe stay under water 15 Seconds; then if the Ball stay 600 Seconds, the depth of the Sea is 933 fathom and 2 foot, if the Ball be found to move equal spaces in equal time.
