ENGINEERING. 



mulative in proportion to the speed, that is, 

 ten strokes in a given time will do more than 

 twice as much work as five strokes in the same 

 time. The boats are very wide, so that the 

 rolling is slight, and the suction pipes are at- 

 tached amidships, so that they are but little 

 affected by the pitching. 



At the close of the season a nearly uniform 

 depth of 26 feet had been secured in a channel 

 about 600 feet wide. Three dredgers similar 

 to the one described were kept constantly at 

 work, their total daily capacity being 6,500 

 cubic yards of solid matter. All the material 

 is taken out to sea and dumped in not less than 

 14 fathoms of water. 



Thus far observations have shown that in- 

 stead of shoaling during the winter, the dredged 

 out channels are slightly deepened by the 

 storms of winter, and there is some reason for 

 hoping that the dike may not, after all, prove 

 to be necessary. 



Lumber-Raft. The launching of a great lum- 

 ber-raft, and its dispersion while en route to 

 New York, in 1887, were recorded in the "An- 

 nual Cyclopaedia " for that year (page 257). The 

 projectors of the enterprise were not discour- 

 aged by failure, but began preparations for a 

 repetition of the experiment on a still larger 

 scale. The port of Joggins, on the Bay of Fun- 

 dy, was as before selected for the building and 

 launching, and the experience gained in former 

 attempts was utilized to the best advantage. 

 The construction was begun in March, and 

 finished about the 1st of July in anticipation 

 of the high spring tides of that month. The 

 logs were laid together in a great cradle con- 

 structed for the purpose. A massive chain- 

 cable ran longitudinally through the center. 

 Its links were 11 inches long and 7 inches wide 

 and If inch thick. At distances of 10 feet 

 radial chains diverged from this central cable 

 and were clamped to cross-pieces on the out- 

 side of the raft. At intervals between the 

 cross-chains, the raft was bound by girths of 

 wire rope. It is evident that when towed by 

 means of a line attached to the central cable 

 the tendency of the stress must be to bind 

 the whole together in a solid ma<s. 



The raft was cylindical, with the ends ta- 

 pered. It was 595 feet long and 150 feet in 

 girth at the midship section. It contained 

 22.000 logs averaging 40 feet in length, and 

 the total weight was estimated at 10,000 to 

 15,000 tons. The expected high tide came on 

 July 25, submerging the seaward end of the 

 raft as it lay upon the ways. 



The raft slid into the water as soon as the 

 blocks were knocked away. "When the enor- 

 mous weight and dimensions of the mass are 

 taken into the account, it is highly creditable 

 to the designer, Hugh R. Robertson, an old 

 lumberman, that the launch was effected with 

 such perfect success. The " Great Eastern," 

 it will be remembered, was only launched aft- 

 er three months of hard work and after the 

 resources of English engineers had been well 

 VOL. xxvui. 20 A 



