50 ANNUAL OF SCIENTIl'IC DISCOVERY. 



something on the same principle as that exhibited in the hull of the 

 Great Eastern steamship; that is, an outer and inner shell, for 

 security and strength. The bottom should be made flat, or slightly 

 arched downward. The whole section would thus resemble that 

 of a gas retort or culvert. 



*' The best plan for placing the tube in position seems to be as 

 follows: as near as possible to the point of crossing it should be 

 constructed by the river side, in a temporary dry-dock formed by 

 earthen embankments, and at such a level that the tide would 

 float it, if admitted by the removal of a dam. The tube should 

 be erected upon timber balks placed crosswise at intervals of 5 

 feet, and bolted to the structure. 



*' These would be floated away with it, and afterward serve as 

 sleepers. 



*' Meantime, the groove in which it was intended to lie would 

 be cut across the channel of the river by dredges. It is no new 

 thing to dredge to an increased depth of 30 feet. It is, in fact, 

 the cheapest method of excavating in all cases where it can be 

 applied. The new Suez Canal has been greatly indebted to the 

 use of dredging in the formation of its approaches. Dredgers 

 have even been made to cut their way into the solid shore, the 

 water following to float them as they made a channel for it. 



•* In the bottom of the groove so prepared concrete must be 

 tipped from barges, and spread to a level by the aid of diving- 

 bells. 



•' When the tube was completed it would be necessary to cover 

 over the ends temporarily to make it water-tight. It would then 

 easily be floated out of the dock to its permanent position. To let 

 in sufficient water to sink it would not occupy many minutes more. 

 The interval between the ebb and flow, which at spring tides is 

 about an hour, would be ample to accomi^lish everything neces- 

 sary. Concrete might then be put in at the sides and over the 

 top, and in this way, assisted by the natural tendency to silt up, it 

 would soon become permanently fixed. Embankments of clay 

 would now be thrown out from the shore on each side of the lino 

 of the approaches, and would join across the end of the tube. As 

 soon as they were made water-tight with clay puddle, the water 

 between must be pumped out and the approaches built in the in- 

 tervening space." — Engineering. 



SYPHON UNDER THE SEINE. 



The city of Paris is now trying to execute a new piece of en- 

 gineering work, which has thus far taxed all their engineers to the 

 utmost. The problem to solve was to unite the two systems of 

 main sewers, which are now nearly finished on both "^ sides the 

 Seine, by means of a syphon. The width of the river at the 

 point to be crossed is 350 feet. Two wrought-iron tubes, each 

 3 feet 10 inches in diameter, were built upon the quay, by the 

 side of the spot to be crossed. Then they were firmly riveted to- 

 gether and made air-tight, closed at both ends and launched side- 



