Page 260 - Third Book of Reading Lessons

READING LESSONS. 259
a glass tumbler; plunge it into water, with the mouth downwards; you will nd that very little water will rise into the tumbler; which will be evident, if you lay a piece of cork upon the sur ce of the water, and put the tumbler over it; r you will see, that though the cork should be carried r below the sur­ ce of the water, yet that its upper side is not wetted, the air which was in the tumbler having prevented the entrance of the water; but, as air is compressible, it could not entirely exclude the water, which, by its
pressure, condensed the air a little.
2. The rst diving-bell of any note was made by Dr. Halley. It is most commonly made in the rm of a truncated cone, the smaller end being closed, and the larger one open. It is weighted with lead, and so suspended, that it may sink ll of air, with its open base downwards, and, as near as may be, parallel to the horizon, so as to close with the sur ce of the water. fr. Smeaton's diving-bell was a square chest of cast-iron, ur et and a half in height, ur et and a half in length, and three feet wide, and a orded room r two men to work in it. It was supplied with esh air by a rcing pump.
3. The sinking and raising of the diving-bell, in­ vented by Dr. Halley, depending entirely on the people at the sur ce of the water, and being besides of considerable weight, so as to occasion much labour, with a risk of the breaking of the rope by which it was to be raised, to the sure destruc ion of those with­ in,-a diving-bell has been invented by fr. Spalding, of Edinburgh, to remedy these de cts, and prevent the edges of the machine om being entangled by any ragged prominences of rock. His machine is of wood, suspended by ropes, and having a leaden weight