MECHANICS AND USEFUL ARTS. 41 



straight line, the sliding tiller traverses back and forward in the eye of the 

 rudder-head, to reconcile the right line action of the nut with the rotatory action 

 of the rudder-head. The effective leverage of the tiller thus becomes greater 

 as the rudder is moved from amidships to either the starboard or port side, 

 and hence the steersman's power is increased in proportion to the external 

 fluid resisted. 



Dempster's Triangular Yacht. A few years since Mr. Henry Dempster, of 

 England, invented a boat of triangular shape, the stern post of which was made 

 to rake at the same angle as the stem, so that both met and terminated at a 

 triangular point under water, and thus formed simply an angular keel. The 

 yacht was twenty feet in length, and had six feet beam, was iron built, aud 

 ballasted with lead. It was rigged with three masts, the main-mast being 

 placed exactly in the centre, and in an upright position : the fore-mast had 

 considerable rake forward, and the mizen-mast the same proportion of rake 

 aft. Two square sails were set on the mam-mast, one above the other, and a 

 triangular sail on each of the other masts ; these triangular sails were on the 

 revolving principle, the booms being secured at the central gravity, one to a 

 pivot on the stem, and the other to a similar pivot on the top of the stern- 

 post ; by which means they would run round and round clear of the masts, 

 and could be trimmed to any degree upon a circle. The sails possessed a 

 double advantage over the common rig, and with the help of the triangular 

 huh 1 could perform many rapid revolving evolutions. Amongst other experi- 

 ments of this triangular yacht was one frequently repeated, in which two 

 stakes were driven into the ground at low water mark, to which a strong iron 

 bar was lashed horizontally like a leaping bar. A pole or gauge was erected 

 alongside the stake-s, marked to feet and inches, to indicate "the depth of 

 water. TVhen the tide rose sufficiently high to show that there was one foot 

 and a half less water than was required to sail clear of the obstruction, con- 

 sequently that the vessel would strike it with her angular keel, she was sailed 

 stem on at the bar, a stiff breeze blowing at the tune, when she went over it 

 by rise and fall, similar to a horse jumping a gate. 



New Methods of Raising Shif)s. A new method of raising ships has been 

 invented by Mr. Foreman, of New York, in -which he employs cast-iron 

 generators, containing wet gunpowder. These are connected with a cast-iron 

 retort or purifier, filled with water, from which passes a coil of cast-iron tube. 

 The whole apparatus is placed in a box about six feet square and two feet 

 high, which is filled with water. From the end of a coil, a hose, dividing in 

 two parts, passes to casks lashed to the sides of the vessel to be operated on. 

 The power in the generator is then ignited, and the gases generated by its 

 combustion pass by means of the hose and pipe into the casks, and displace 

 the water with which they are filled, holes having been made in the bottom 

 of the cask. The buoyancy thus produced by the confined air is what raises 

 the vessel. 



A novel variety of lifting tanks for raising sunken vessels has recently been 

 invented by Capt. Bell, These, combined, are a novel and curious apparatus 

 being two separate water and air-tight tanks, with straight or square sides, 

 each having on its outer side the form of an acute angle ; while the inner 



