4-1, On the Diving- Bell. 



joining water in a pipe; or an additional bell might be used 

 of such a form as to expose a great surface to the water, in 

 which it should be frequently moved about. It is worthy of 

 remark, that any substance which would absorb vapour as 

 before suggested, would also tend to cool the air. A metallic 

 bell by conducting heat more quickly has an advantage over 

 wood. 



3. The generation of carbonic acid is the great cause of air 

 being wasted; air becomes unfit for respiration by a small 

 admixture of carbonic acid. Agitation in water will be of 

 little use towards the absorption of the acid; lime-water might 

 be more successful. 



4. The want of oxygen: — This is generally sent down 

 [mixed with azote in the form of -common air J from the sur- 

 face in barrels, or by a condensing pump ; and no method can 

 be better where the bell is fixed, a constant circulation of air 

 obviating all the former difficulties, and not occupying the 

 time of the persons otherwise employed below. Air may, 

 however, be drawn down from above. If for instance, a pipe 

 from the surface were to communicate below with the clack- 

 hole of a common pair of bellows, and if there were a valve 

 opening outwards fixed at the nozzle, then on opening the 

 bellows the air would rush down the pipe, and on closing them 

 would be driven out at the nozzle into the bell. The air in 

 the pipe will not be of the same density as the air in the bell, 

 on which account the pipe must not be formed of leather, or 

 any substance which will yield to the pressure of the water. 

 Some naturalists describe insects which rise and fall in the 

 water, and are connected with the surface by a tube of variable 

 length. Perhaps ultimately the oxygen will be supplied by a 

 chemical process from the surrounding water, or from the 

 black oxide of manganese, or condensed fluid oxygen, or some 

 other substance taken down in the machine. 



I will add two remarks on the most valuable memoir above 

 referred to. 



1. When the bell rises to the surface, the aqueous vapour 

 condenses into a cloud. Does not this partly arise from the 

 cold which mere rarefaction of air produces, by changing the 

 capacity for heat? 



2. In the proposal for giving motion and direction to a 

 diving-boat, would it not be better to follow nature in the for- 

 mation of fishes. Nature has placed fins at the sides of the 

 animal in most cases. Locomotion is produced by the tail in 

 a manner not generally understood ; it is bent slowly, and re- 

 turned to its straight position with great rapidity; as the re- 

 sistance varies nearly with the square of the velocity, the force 



lost 



