MECHANICS AND USEFUL ARTS. 61 



necessary to find a compensation. The inventor thinks he has found 

 a perfect one, which consists in applying a second column of water 

 and air to press upon the other surface of the mercury, that in the 

 glass tube. This second column is precisely like the first, as regards 

 the pipe and cylinder, and communicates with the sea by an aperture 

 or apertures, presented in such a direction that the velocity does not 

 produce any increase of pressure. Thus the mercury in the indicator 

 is placed between two columns of water and air, which are always 

 equal to each other in length, and the mercury rises according to the 

 difference between the pressures upon its two surfaces, the result of 

 resistance or velocity alone. The air-pipes may be conducted in any 

 direction, and the indicator, which swings upon gimbals, may be 

 placed in any part of the ship. The two water-pipes are conducted 

 into one in the bottom of the ship, divided into two separate chambers 

 for the different forces. The true course, or leeway of the vessel, is 

 also indicated upon a horizontal segment divided into degrees, over 

 which a needle is moved by a rod connected with the above-mentioned 

 double tube ; and the whole is kept continually in the true direction 

 of the ship's motion by a float or vane attached to the lower end of the 

 tube in the water. Brewster's Philosophical Magazine, July. 



WATER-METER. 



AT the meeting of the Scottish Society of Arts, on April 22, Mr. 

 F. A. Bucknall described a new meter, designed for the measurement 

 of the supply of water to private dwellings, &c. It consists chiefly 

 of a fan-shaped bucket-wheel, revolving within a cylindrical case, and 

 kept water-tight by means of a packing of India-rubber, leather, or 

 other elastic substance, supply and delivery pipes, and wheel and 

 pinion-geer, \vhich is connected with an index-plate. The revolving 

 action of the meter is maintained by the gravity of the wheel being 

 constantly greater on the one side than on the other, owing to the 

 continuous running off of the water from the opposite side to that at 

 which it is supplied. The meter is only in action while the water is 

 running off. Civil Engineer and Architect's Journal, July. 



SELF-REGISTERING TIDE-GAUGE. 



MR. MEIK has described to the Scottish Society of A.rts a new 

 self-registering tide-gauge, lately erected in Sunderland Harbour. A 

 well, carefully boxed in, and of exactly similar depth to the water on 

 the bar, is made below the building containing the apparatus. Within 

 this well, in an interior pipe or trunk, and rising and falling with the 

 tide, works a float suspended by a copper-wire cord, which is carried 

 over a spiral cone fixed in an upper story of the building. By the 

 simple arrangement of a wheel and pinion at the opposite end of the 

 axle to which the cone is fixed, a web of wire-gauze works on two 

 rollers fixed at its upper and lower ends. The lower roller is regu- 

 lated by the movement of this wheel and pinion, the upper one by a 

 balance-weight attached to a copper-wire cord, which also passes over 



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