366 



J/r. Leonard Hill 



[May 25, 



(1839) applied it to the sinking of excavation through quicksands, 

 and the bell became evolved into the modern caisson — a steel chamber 

 provided with a cutting edge below, and an air-lock above for allowing 

 the men to enter and leave without raising the bell. Finally the 

 caisson was applied to the purpose of horizontally tunnelling under 

 rivers. To effect this a steel shield provided with cutting edge, is 

 driven forward by hydraulic jacks. Screens are placed in the shield 

 to allow excavation of the soil in front of it. As fast as the shield is 

 driven forward, segments of the iron tunnel are built into place. 

 Water is kept out of the work by the use of compressed air. On 

 entering, the men are " compressed " in the air-lock, i.e. the air- 

 pressure is raised to that in the tunnel, and on leaving the tunnel 

 they are " decompressed," i.e. the air-pressure is lowered in the lock 

 down to the normal, so that the outer door of the lock may be 

 opened. 



A diver is " compressed " on descending into the water, as the 

 pressure of his air-pump always keeps up to that of the water. On 

 coming up he is " decompressed." 



The workers in compressed air from first to last have suffered 

 from illness and loss of life. The higher the pressure, the greater 

 the loss. Thus there occurred at : — 



I 



Douchy mines (shaft sinking) 

 Kehler bridge (Rhine) . . 

 Adour bridge 

 St. Louis bridge (Mississippi) 



Brooklyn bridge , . 



Toulon dry dock . . 

 Cubsac bridge 

 Eider bridge 

 Nussdorf works (Danube) 



Felesti bridge (Danube) . . 



Hudson tunnel . . 



63 cases (Pol and Watelle). 



133 cases (Francois). 



90 per cent, of workers (Limousin). 



119 cases out of 352 workers ; 50 



cases of paralysis ; 14 deaths (Eads, 



Jaminet). 

 110 cases in 4 months and 3 deaths 



(Smith). 

 43 cases in 3 weeks and 2 deaths. 

 104 cases and 3 deaths (Gerard). 

 38 cases and 2 deaths (v. Haller). 

 320 cases among 675 workers 



(v. Schrotter). 

 55 cases and 5 deaths among 154 



workers (Tine). 

 1 man died a month among 50 



workers, until the conditions were 



altered (E. W. Moir). 



At New York, Mr. E. W. Moir tells me, 8 men have died in tlie 

 last 6 months, and there have been many severe cases besides. 



Many cases of illness and death occur also among deep-sea divers. 

 Catsaras (1890) published accounts of 70 cases collected from the 

 Greek sponge divers. He averaged the deaths as 10 per annum in 

 the sponge fisheries of Hydra. Compressed air sickness is charac- 

 terised by its protean symptoms. Catsaras records cases of loss 

 of speech, blindness, deafness, transitory madness, vertigo, loss 

 of consciousness, subcutaneous emphysema, spinal paralysis, etc. 



