DIVING BELL. 125 



But the first Bell of any note, was one made by Doctor flalley, and is 

 most commonly represented in the form of a tunicated cone, the 

 smallest end being closed, and the larger one open. It is weighted with 

 lead, and so suspended that it may sink full of air, with its open base 

 downwards, and as near as may be parallel to the horizon, so as to be 

 close to the surface of the water. 



Mr. Smeaton's diving bell was a square chest of cast iron, four feet and 

 a half in height, four feet and a half in length, and three feet-wide, and 

 afforded room for two men to work in it. It was supplied with fresh 

 air by means of a forcing pump. This was used with great success at 

 Ramsgate. 



The diving bell invented by Messrs. Cottam and Hallen, which is 

 shown daily at the Polytechnic Institution, Langham Place, Regent Street, 

 is composed of cast iron, open at the bottom, v/ith seats around, and is 

 of the weight of three tons; the interior for the divers is lighted by open- 

 ings in the crown, of thick plate glass, which is firmly secured by brass 

 frames, screwed to the bell; it is suspended by a massive chain to a large 

 swing crane, with a powerful crab, the windlass of which is grooved 

 spirally, and the chain passes over four times into a well beneath, and to 

 which is suspended the compensation weights, and is so accurately arranged 

 that the weights of the bell is, at all depths, counterpoised by the 

 weights acting upon the spiral shaft; the bell is supplied with air by two 

 powerful air pumps, of 8 inch cylinder, conveyed by the leather hose to 

 any depth. 



To illustrate the principle of Messrs. Cottam and Hallen's diving bell, 

 you have only to take a glass tumbler, plunge it into water with the mouth 

 downwards; you will find that very little water will rise into the tumbler, 

 which will be evident if you lay a piece of cork upon the surface of the 

 water, and put the tumbler over it, for you will see that though the cork 

 should be carried far below the surface 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 the air is compressible, it could not entirely 

 preclude the water which, by its pressure, condensed the air a little. 



Mr. Spalding's bell varies considerably from the above. It has a 

 bell-like form, and is suspended by four ropes, with ballast weights, by 

 means of which the mouth of the bell is always kept parallel to the 

 surface of the water. By these weights alone the bell, however, will not 

 sink ; another is therefore added, by means of which it can be raised or 

 lowered at pleasure. In descending, this balance weight hangs consider- 

 ably below the bell in case the edge of the bell is caught by any 



