An Appendix to the Directions for Seamen, bound for far Voyages.
Whereas it may be of good use, both Naval and Philosophical, to know, both how to sound depths of the sea without a Line, and to fetch up water from any depth of the same; the following waies have been contrived by Mr. Hook to perform both; (which should have been added to the lately printed Directions for Seamen, if then it could have been conveniently done.)
First, for the sounding of depths without a Cord, consider Figure 1, and accordingly take a Globe of Firr, or Maple, or other light Wood, as A: let it be well secured by Vernish, Pitch, or otherwise, from imbibing water; then take a piece of Lead or Stone, D, considerably heavier then will sink the Globe: let there be a long Wire-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 ring E, and so let Globe and all sink gently into the water, in the posture represented in the first 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 reascend. And, by observing the time of the Ball's stay under water (which may be done by a Watch, having minuts and seconds, or by a good Minut-glass, or best of all, by a Pendulum vibrating seconds) you will 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 Tryals already made with this Instrument, the Globe being of Maple-wood, well covered with Pitch to hinder soaking in, was 513/16 inches in diameter, and weighed 2½ pounds: the Lead of 4½ pounds weight, was of a Conical figure, 11. inches long, with the sharper end downwards, 19/16 inches at the top, and 1/16 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 thereabout: From many of which kind of Experiments it will likely not be hard to finde
out a method to calculate, what depth is to be concluded from any other time of the like Globes stay under water.
In the same Tryals, made with this Instrument in the said River of Thames, it has been found, that there is no difference in time, between the submersions of the Ball at the greatest depth, when it rose two Wherries length from the place where it was let fall (being carried by the Current of the Tide) and when it rose within a yard or so of the same place where it was let down.