Mr. Mackain on Eximgvishing Fvres. 15 



surface of the water in the water vessel, and the valve, h, being thereby 

 shut, the water will be forced along the pipes, wi, n, to the same height 

 above the water vessel, as the distance between the surfaces of water 

 in the cistern and air vessel 



Thus, if the air vessel be at the level of the ground, — the surface of 

 water in the cistern be 30 feet above it, — and the water in the water 

 vessel, 26 feet above the ground, — water will flow from the conduit- 

 pipes at the height of 55 feet above the ground ; and the pipes might 

 be made to discharge any required volume, in a given time, below this 

 point, by a proper adjustment of the diameters of the pipes, and of 

 the diflference between the several water surfaces. The velocity of 

 discharge helow the cistern, is that due to the extreme height to which 

 the compressed air can raise the water in the upright pipe. 



When the upper vessel is exhausted, the stop-cock, A, on the pipes 

 leading from the cistern, is to be shut ; the stop-cock, t, for discharg- 

 ing water from the air vessel, is to be opened ; and the pressure being 

 now taken off the water vessel, the valve, b, on the feeding pipe, will 

 be opened by the water in the cistern ; the water vessel will be charged, 

 and the apparatus be again ready for use. 



I understand that this machine is so arranged in Hungary that it is 

 self-acting. It, therefore, would only require a stop-cock on the con- 

 duit-pipes, to be opened or to draw water in the event of fire, to set it 

 in motion, — an instantaneous aid that, in such cases, is invaluable. 



The greater size of the lower vessel is necessary to admit of the com- 

 pression of the air to the requisite extent, and at the same time that 

 there shall remain a bulk of compressed air equal to the contents of the 

 water vessel, so as to expel the volume of watqi^ith which it was filled. 



As air compresses into one half of its bulk, with a weight equal 

 to that of the atmosphere, or of a column of water 33 feet in height^ 

 it follows, that by this apparatus only one half of the quantity of water 

 which falls from the cistern into the lower air vessel, can be raised to the 

 height of 33 feet above the water vessel, or 66 feet above the ground ; 

 and following out the law of compression, only one fourth of the quantity 

 could be raised to 99 feet above it, or to 130 feet above the ground. 



These are heights not usually coming within the scope of ordinary 

 cases, in the circumstances now in view; but the pressures due to 

 these heights can be produced by multiplying the number of cylinders 

 on the same levels, and thus forces of great intensity, though of moderate 

 ranges of extent, could be obtained by this apparatus, and rendered 

 available for many purposes connected with manufactures and the arts. 



(Mr. Mackain exhibited a model of this apparatus, in which the 

 receivers were 4^ feet apart, and a flow of water was produced from 

 pipes connected with the water vessel, at the same height A second 

 pair of receivers were connected; and tlie pressure, amounting to 

 double of the first pair, was exhibited by a column of mercury.) 



