28 ANNUAL OF SCIENTIFIC DISCOVERT. 



ure, lacking only the proposed dam at its lower end to make an 

 enormous basin and to convert the rapids into a smooth mill-pond 

 or rather lake, with a semi-Niagara at its outlet, and a hydraulic 

 power estimated as 2,000,000 of horses. There is also another 

 natural channel running between the islands, which admits of 

 being made into a mill-stream of 75,000 horse-power. To com- 

 plete the work of nature in this way, requires a dam 2,800 feet in 

 length, leaving the southern and only navigable channel open for 

 commerce, and the shoal, rocky bed of the river below the dam, 

 besides the shore, for the accommodation of a city of mills and 

 factories. A great canal is also to be led inland from the new 

 lake, to supply other factories and conduct au abundance of water 

 to the city. Scientific American . 



A DAM BUILT IN MIDWINTER. 



Among recent engineering operations, the construction of the 

 dam at Turner's Falls, Mass., on the Connecticut River, in the 

 depth of winter, is somewhat interesting. The channel being 

 divided by an island, the work, a dam of 23 feet in height and 900 

 feet in length, was built in two sections, one after the other; an 

 opening, 12 feet lower than the dam and 200 feet wide, having 

 been left in the middle of the first section, for the passage of the 

 current while the second section was building. But before the 

 second section had been completed (which was done by the 

 middle of December last) a freshet brought down a raft of timber 

 against a wooden barrier, erected to guard the opening left in the 

 first section, and to facilitate finally closing it, and, sweeping away 

 this structure, tore out the foundations of the dam below the 

 opening, down to the bed-rock, for a breadth of about 110 feet. 



This breach must be repaired at once or the whole remaining 

 work was liable to be swept away by a freshet at any time in lute 

 winter or spring. The ordinary flow of the river through the 

 breach was 5 to 8 feet deep, with a velocity of 10 to 12 feet per 

 second, and a volume, as estimated, of 5,000 to 10,000 cubic feet 

 per second. To turn the water out of this channel, that the 

 masonry might be laid in its bed, a provisional dam was con- 

 structed of timber cribs, bearing against the stream in the form 

 of an arch, and spanning horizontally the breach. The first crib 

 or pier was towed into position on the 31st of December, and 

 sunk b} T filling with stone. Ten such piers were placed at equal 

 distances, ends against the current, as radii in a segment of a 

 circle, and the last was in position on the 16th of January, 1867; 

 the current still flowing freely between them. The passages 

 were now to bo closed by a second set of piers, tapered to fit the 

 convergence of the first set, and serving at once to key and fill the 

 arch, which then presented a front to the current only con- 

 solidated the more the greater the pressure brought against it. 

 The last of these plugs was put in on the 1st of February. 

 Nothing remained but to fill in and tighten the barrier, after 

 which the dam was laid in perfect security, commencing March 

 1st and finishing on the 22d of that mouth. The work of filling 



