1884. 65 . Trails. N. V. Ac. Sci. 



favor it. It would not fall, because it would have to stem an oppos- 

 ing current. Prof. LOOMIS has pointed out the existence of a dry belt 

 on either side of the equator, and the need of air from the tropics, 

 coming over the water, e.g., the Gulf of Mexico, and so coming north- 

 ward, loaded with moisture, to be here deposited as rain. Thus any- 

 thing thrown into the atmosphere in the region of ascending currents 

 could be readily carried up. 



Mr. F. CoLLiNGWOOD exhibited a sample of curiously corroded iron 

 wire. He had been called upon to examine the cables of the Suspen- 

 sion bridge at Pittsburg, built about twenty-four years ago by the 

 elder ROEBLING, and to superintend the repairs. The cables, where 

 they enter the anchorage, were enclosed in heavy canvas, filled solidly 

 with coal-tar which had been boiled and treated with quick-lime. A 

 brick wall was then built on each side of each cable, and the whole 

 space between these and around the mass of wire and coal-tar was 

 filled with cement mortar. Over this was a layer of heavy flag-stones 

 laid in cement, and over this the flags of the side-walk. In some way, 

 in the lapse of time, a considerable portion of the tar at each cable end 

 had disappeared, and the cavity thus left contained in every case a 

 dirty brown liquid, in some cases nearly filling the cavity. The mys- 

 tery was whence the liquid came. One theory was that the coal-tar 

 had undergone a slow distillation by the heat of the sun, striking on 

 the flagging above. The liquor contained various salts of ammonia, 

 among them the sulphide being quite prominent. His own idea was, 

 that the high temperature acquired during a hot day would make the 

 tar very liquid, and it would then (as was found) penetrate the brick- 

 work and leave a cavity. 



This cavity would be filled with air, which, at the high temperature 

 of a summer's day, would be expanded and a portion forced out. This 

 would be pumped in again by the cooling down which takes place at 

 night ; and, when the air was highly charged with moisture, a part of 

 this would be condensed and remain in the cavity. 



This would account also for the sulphur, which is no doubt diffused 

 in sensible amounts in the atmosphere of Pittsburg from the large coa 

 consumption. The wire seizings were jonu of an inch in diameter, an ' 

 were in many places rusted through. There were several wires rusted 

 off in each cable. Nearly all the exterior wires in each strand were 

 corroded somewhat, and it was thought best to cut and repair about 

 500 of them. The masonry was cut out, and tunnels built so as to af- 

 ford ready access to each cable in the future. The cables were un- 

 wrapped for about 15 feet outside of the masonry and every wire thor- 

 oughly cleaned. In every case, before putting on the wrapping again, 

 the cables were saturated with boiled oil and white lead. 



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