Chapter I 

 HIGH PRESSURE 



1. Diving bells. 



At the beginning of the sixteenth century Sturmius invented 

 the diving bell, which was to render such great services. It was 

 simply a bell heavily weighted, which, full of air, was allowed 

 to sink vertically in the water until it touched the bottom. The 

 water penetrated the apparatus to a height which increased with 

 the depth of the immersion: at ten meters, there was under the 

 bell, in volume, half air and half water; at twenty meters, two- 

 thirds water and one third air, etc.; the workmen, who were 

 ensconced up to that point on seats like shelves, got down from 

 them to work under the worst conditions. 



The inventor considered the harmful effect which the air com- 

 pressed by the descent might exert upon them; to prevent it, says 

 Panthot, 1 he advised that air should be taken along in bottles 

 which would afterwards be broken under the bell. 



This procedure, which could not alter at all the tension of the 

 air, was improved upon by Halley, with a purpose in greater har- 

 mony with the laws of physics. The English physician planned 

 to drive out the water which encroached upon the workman and 

 to renew the air which had been made foul by his respiration; he 

 'did so by letting down under the bell small barrels full of air, 

 which the diver received and opened at will; the warm and foul 

 air escaped from the top of the bell by means of a valve. Halley 

 even found the means of permitting a diver to leave the bell, 

 keeping in communication with the compressed air contained in it 

 by mean of a tube and a helmet covering the head. (Brize-Fradin, 

 2nd. S., pi. I.) . This was the first idea of the diving suit. 



Spalding made improvements of a purely mechanical type in 

 Halley 's apparatus; these improvements did not prevent him from 

 meeting death in his own apparatus in 1785. 



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