MECHANICS AND USEFUL ARTS. 43 



no obstructions to navigation and the tides, and that it would be 

 removed from danger of disturbance from floating ice and from 

 gules, is susceptible of proof. Its cost, estimated at only about 

 8^00 per running foot, is so much less than that of any bridge, 

 that 12 of these tubes could be laid for the cost of a single 

 bridge. Its approaches could be close to the shore, and therefore 

 not interfere with he rights of property owners. In every aspect 

 the submerged tube appears to be better than the aerial bridge. 



Subsequently, as seen in No. 39, Vol. xn., 1857, "Scientific 

 American," we published engravings of a similar plan, suggested 

 by H. P. Holcomb, of Winchester, Ga., and the engravings rep- 

 resent a profile view and the entrances, style of tube, and a cross 

 section. 



The plan of building the tubes proposed is similar to that fol- 

 lowed in the construction of the Pneumatic Tube in London ; that 

 is, that it be built in sections, the ends of which are made water- 

 tight, and then the sections floated to place and sunk by admitting 

 a sufficient quantity of water, to be afterward pumped out. The 

 joints to be made by bolted flanges. 



We see fewer objections to this style of crossing rivers, espe- 

 cially when very wide or where a bridge must be very elevated, 

 than to any other. If the tube is sunk in a bed dredged for it 

 there can be no reason why it might not last for generations, es- 

 pecially if, like that of the Thames, it is protected externally by 

 courses of brick masonry. No objection to the submerged tube, 

 except the fact of its situation, would, seem to obtain which might 

 not be equally valid when urged against the elevated bridge. 

 Certainly teams and street railway cars could as readily traverse 

 the tube as the bridge. In either case there must be an ascent 

 and a descent. But, beyond the fact of less cost in favor of the 

 tube, there is the superiority in case of approach and the conse- 

 quent shortening of the distance. The two plans seem at least 

 worthy comparison by those interested in the subject. Scientific 

 American. 



A TUNNEL THROUGH A VOLCANO. 



English engineers have nearly completed a railway tunnel 

 through a volcanic range in New Zealand. The plains of the 

 Canterbury settlement, in the southern of the two great islands of 

 New Zealand, are divided from the port of Lyttleton by almost 

 impracticable hills, and in May, 1861, the local government ac- 

 cepted an offer to complete a line of railway from Lyttleton to 

 Christ-church in 5 years ; the cost of a tunnel 2,838 }*ards long, 

 and called the Moorhouse Tunnel, being fixed at 195,000. The 

 works were at first carried on under great disadvantages, on ac- 

 count of the Otago gold fever and other causes. 



This tunnel affords, it is believed, the first instance where a 

 complete section of an extinct volcano has been opened out. The 

 rock in the tunnel is a series of lava streams and beds of tufa, in- 

 tersected by vertical dykes of phonolite. The lava streams gen- 

 erally consist of scoria, overlying a coarse pink trachyte, which 



