VOL. XXXIX.] PHILOSOPHICAL TRANSACTIONS. Id 



To obviate this inconvenience, he caused a spiral tube of copper, be, to be 

 placed close to the inside of the bell, so fixed that it may be easily taken out 

 and cleansed at pleasure ; and at the same time not to incumber the diver in the 

 bell. At the upper end of this tube, a flexible leather tube is joined, 1 feet 

 long; at the end of which is a turned ivory mouth-piece, which the diver, as 

 soon as he perceives the air to grow hot in the top of the bell, keeps constantly 

 in his mouth, which he is able to do in any position, by means of the flexible 

 tube, standing, sitting, bowing his head, &c. And all the while he draws his 

 breath through it, and the air from c; by which contrivance he not only draws 

 continually cool and fresh air as long as any is in the bell, but occasions at the 

 same time a circulation, which is so necessary to the very being of air, espe- 

 cially in a compressed state, and its preservation for the use of animals; and so 

 much the more necessary, as any body who has been in a diving bell for a long 

 time without any new supplies of air, and has been reduced to the last extre- 

 mity of breathing in it, will agree, that when at such a time the bell begins to 

 be drawn up, and by that means the compressed air allowed to expand, and be 

 put into motion ever so little, the man receives as it were a new life, and incre- 

 dible comfort and ease. 



Again, when, in coal-pits, levels are driven in the coal, or through dykes, 

 the air of the level or adits growing hot by the breath and sweat of the hewers 

 and workmen, for want of a circulation of the air; he has found it to be an 

 excellent remedy, to place along the side of the drift or adit, a square wooden 

 box, open at both ends, laid from the place where the air is cool and good, 

 reaching as far, by joining one box close to another, as where the work is car- 

 ried on. Thus, by this simple contrivance, a circulation of air is obtained, and 

 sometimes to that degree, that when a candle is held at the end of the box 

 where the cool air enters, the flame is driven out by the current of cold air 

 entering and circulating through the box. 



By which experiment he thinks, that though the diver should not keep the 

 end of the flexible tube in his mouth, which he may easily do, yet that the air 

 would circulate through the copper tube, and he will receive no small benefit by 

 it. DD are the weights for sinking the bell, so contrived as easily to be hooked 

 on the same hanging on the cable. The iron plate e, fixed to the chains fff, 

 serves the diver to stand upon, when he is at work. 



The bell is very well tinned on the inside; and as in all rivers, and the coasts 

 of the Baltic, the water is exceedingly clear and limpid, because there is no 

 ebb and flood, M. Triewald has placed strong convex lenses gcg ; by which 

 means the diver can not only see what is under him, but also on all sides at a 

 good distance. 



These glasses have strong copper lids, hhhh, like snufF boxes, which are 



