Page 261 - Third Book of Reading Lessons

260 THIRD BOOK OF
appended to it, by means of which the mouth of the bell is kept always parallel to the sur ce of the wa­ ter, whether the machine, taken altogether, is lighter or heavier than an equal bulk of water. By these wejghts alone, however, the bell would not sink; another is there re added, which can be lowered or raised at pleasure, by means of a rope passing over a pulley, and stened to one of the sides of the bell. As the bell descends, this weight, called by Mr. Spalding the balance-weight, hangs down a consider­ able way below the mouth of the bell. In case the edge of the bell is caught by any obstacle, the bal­ ance-weight is immediately lowered down, so that it may rest upon the bottom. By this means the bell is lightened, so that all danger of Versetting is re­ moved; r, being lighter without the balance-weight than an equal bulk of water, it is evident that the bell will rise as r as the length of the rope a xed to the balance-weight will allow. it. This weight, there re, serves as a kind of anchor to keep the bell at any particular depth which the divers may think necessary; or, by pulling it quite up, the descent may be continued to the very bottom.
4. By another very ingenious contrivance, fr.
Spalding has rendered it possible r the divers to
raise the bell, with all the weight appendjng to jt,
even to the sur ce of the water, or to stop it at any
particular depth, as they think proper ; and thus they
..
would still be sa , even though the rope designed r
pulling up the bell should be broken. For this pur­ pose, the bell is divided into two cavities, both made as tjght as possible. Just above the second bottom are small slits in the sides of the bell, through which the water entering as the bell descends, displaces the air originally contained in its cavity, which ies out