1896.] on the Tunnel under the Thames at Blachwall. 93 



river at Blackwall Cross, about 8 feet below the street level, a human 

 skeleton was found, and as a stake was also found which appeared 

 to have been driven through the body at the time of burial, in 

 all probability the remains were those of some poor suicide who 

 had been interred with all the superstitious rites of our ancestors. 

 Beyond the above I do not think anything of interest has been 

 discovered. 



Experience of Compressed Air. — In some previous works carried 

 out under compressed air, oiuch illness and some deaths have occurred. 

 The symptoms of the more frequent though not serious illnesses are 

 violent and acute pains of a neuralgic kind, generally in the limbs, 

 and which are experienced at the time of, or shortly after coming out 

 of compressed air. The more serious, and in some instances fatal 

 cases took the form of vertigo and paralysis, usually of the legs. 

 Consequently at an early period the London County Council adopted 

 every precaution ; they obtained Parliamentary power to compensate 

 persons permanently or temporarily injured, and they appointed a 

 resident medical officer. Dr. Snell, whose duty it was not only to 

 attend to cases of illness, but to see that none but healthy men were 

 allowed on the work, and to keep a watch on all the men employed 

 in compressed air, besides which he was instructed to note from a 

 medical point of view, and make a study of, all the conditions of the 

 problem. We have now been at work under compressed air for about 

 two years, we have had no deaths and only one case of permanent 

 injury (a case of Menier's disease, due to rupture of the semicircular 

 canal of the inner ear). It had often been noticed, on previous works, 

 that illness was most prevalent when the work progressed most 

 slowly, and that it decreased as the progress became more rapid. 

 We now believe, from our experience at Blackwall, that this was due 

 to the larger amount of air pumj)ed down during rapid work. With- 

 out for a moment wishing in any way to forestall Dr. Snell, who 

 will no doubt make public the result of his observations at the 

 proper time, we believe that up to a pressure of from 30 lbs. to 

 35 lbs. per square inch, healthy men can work with almost an entire 

 absence of illness, if a sufficient amount of compressed air, say 8000 

 to 9000 cubic feet per hour, be supplied to each man. 



Conclusion. — In drawing this discourse to a conclusion, I feel 

 that I have but very imperfectly performed the duty which I have 

 undertaken. We have now completed all the work on the south side, 

 the river has been passed, and we are working up the incline near 

 shaft No. 1, and if all goes well we hope to comj^lete the whole by 

 about March next year. In contemplating the work at Blackwall it 

 is interesting to compare the progress in engineering work during 

 the past fifty years. Brunei's tunnel was about the same length 

 as the |)()rtion under the river at Blackwall, and it took about nine 

 years, with many long pauses, to complete ; the portion of the Black- 

 wall tunnel under the river between shafts 2 and 3 was tunnelled in 

 about thirteen months. The cost of Brunei's tunnel was at the rate 



