652 



HISTORY OF THE SEA. 



anima 1 . ; they saw that each of themselves carried on this process 

 constantly, but what they breathed they did not know, and 

 they were equally ignorant of why they breathed. The dis- 

 covery of what the air is belongs purely to modem tunes 

 About a century ago the astronomer Halley first proposed the 

 use of the diving- oell, and went down in one he had built, tc 

 the depth of about fifty feet. The diving-bell was named from 

 its original form, which was that of a bell, and this name ifi 



DIVING-BELL. 



still retained, though the form of the vessel is changed. The 

 supply of air is kept up by an air-pump worked above water. 

 This is, however, a clumsy appliance in which the diver ia 

 limited only to that portioi of the bottom on which the bell 

 raits. Where there is either a strong current, or the bottom 

 is very shelving, the diving-bell is embarrassing if not danger 

 ous. In one case it is said that the diver was taken from the 

 bell by a shark. Expert swimmers can dive from the outside, 

 and, passing under the lip of the bell, rise suddenly inside of 

 it, a feat which always surprises those who are in the bell 



