jointly, and constructed by them, with the aid of Mr. Sharp and Mr. Jackson, was shaped like a cigar, over one hundred feet long and twenty feet in diameter at the thickest part. It was divided into many compartments, all water-tight, so that if one or even three were flooded the ship would still be useable.
Buoyancy was provided for by having several tanks for the introduction of compressed air, and there was an emergency arrangement so that a collapsible aluminum container could be distended and filled with a powerful gas. This was to be used if, by any means, the ship was disabled on the bottom of the ocean. The container could be expanded and filled, and would send the Advance to the surface.
Another peculiar feature was that the engine-room, dynamos and other appartus were all contained amidships. This gave stability to the craft, and also enabled the same engine to operate both shafts and propellers, as well as both the negative forward electrical plates, and the positive rear ones.
These plates were a new idea in submarine construction, and were the outcome of an idea of Mr. Swift, with some suggestions from his son.
The aged inventor did not want to depend on the usual screw propellers for his craft, nor did
