MECHANICS AND USEFUL ARTS. 39 



pended on one side, with which she floated with great ease. There was 

 afterwards placed in the boat 500 pounds of iron, then she was filled with 

 water, and four sixty-four pound weights suspended on one side, under which 

 pressure she floated with her gunwales six or eight inches above water. She 

 was put together and launched in two minutes. The following is a brief 

 description of the boat ; She is made of a strong frame of wood, modelled like 

 an ordinary boat, covered with canvas coated with gutta-percha, a large air 

 compartment in the shape of a cylinder outside the boat, i*unning from, stem 

 to stern along the gunwales. .The gunwales and ribs are hinged to the keel, 

 so that when the boat is not required for use, the ribs can be thrown parallel 

 with the keel, and thus allow the gunwales to fall down on both sides close 

 to the keel, compressing the boat in about a fifth its size when ready for use." 



:NEW PLAN FOE LOWEBIXG BOATS AT SEA. , 



Mr. Clifford, of London, has invented an ingenious plan for lowering boats 

 from a vessel's side in perfect safety at sea, in any weather. The unlashing, 

 lowering, and disengaging are done by one man only in the boat, whose sim- 

 ple weight is made to hold hi equilibrium, the weight or descending momentum 

 of the boat with its entire crew, which he has thus the power to check or con- 

 trol at will. The process is as follows : One man in the boat unhitches a rope 

 from a cleet (on the boat's seat) over which he slackens it off. The boat 

 descends levelly, both laterally and longitudinally, frees itself from the gripes, 

 by which it was firmly lashed to the ship's side (if there is not time to unfasten 

 them), and letting go the rope disengages the boat from the ship. The lowering 

 may be effected as well from one as two davits, or from a yard or spar, and with 

 any degree of velocity, which can be checked at any part of its descent, and 

 with the vessel going at any speed. A hollow rotary plug fixed at the bottom 

 of the boat allows the free ingress or egress of water, which a half-turn stops ; 



the plug is consequently never out of its place. 

 * 



IMPKOVEMEXTS ES" NATAL AECHITECTCTIE. 



Iron Tubular Ships. James Hodgson, of Liverpool, England, is now build- 

 ing iron screw steam-ships on a principle for which he has taken out a patent. 

 These vessels are constructed without frames, side-frames, floorings, &c., in 

 dispensing- with which it was found necessary to increase the strength of the 

 plating for the sides ; but to double the strength it is not necessary to double 

 the thickness of the plate, as the strength of the materials increases as the 

 square of the thickness. The strength is further increased by a bulkhead 

 being placed in the widest part of the ship, amidships, and by other bulk- 

 heads placed midway between the midship bulkhead and the bow and stern, . 

 and again by the interposition of stiffening plates, so as to spread the strain 

 along the vessel's side from one to four feet from the bulkhead. As the 

 sides of the ship, under ordinary circumstances, are much weakened by the 

 holes cut for the bulkheads to be secured to, the patentee extends the butting 

 'piece, usually placed over the joint, along the line or strake of plates, and 

 spreads the rivets over a wider area. By the construction of a ship in this 

 manner in fact, on the principle of a huge steam-boiler or tube, with rounded 



