262 Mr. MacKain on the Compression of Water. 



square root of the force employed to propel it. As gas, after having 

 been propelled through a range of pipe, and when escaping from its 

 extremity into the air, will be only of the density due to the pressure 

 of the atmosphere — the portion of it at the origin of the pipe, or, as is 

 usual in practice, that in the gas-holder is not only of the density of 

 the atmosphere, but is also of that further degree of compression due 

 to the force applied for its propulsion through the pipes. In all 

 experiments made with pressure-gages along various lengths of pipes, 

 this extra degree of compression is found to diminish according to the 

 square root of the length of the pipe, thus showing a gradual relaxation 

 of compression, and a steady progression of current. 



The ascertained laws of impulsion and of retardation of gas and 

 water being thus exactly alike, it only now remains to ascertain their 

 measure ; and if these be found proportional to their density, there 

 appears reason to believe, that water, under proportional forces, is as 

 compressible as air. 



I shall endeavour to support these views by the following facts, and 

 deductions from them: — 



As water is 825 times heavier than air, the velocity communicable 

 to air contained in a pipe by the pressure of one vertical inch of water 

 is equal to that of 825 vertical inches, or 68 feet of air ; and if gases 

 be referred to, as their specific gravity is usually compared with air, 

 as 1, the height of a corresponding column of any gas is equal to 68 

 feet divided by the specific gravity of that gas ; thus, one inch of water 

 is equal to /^^^=122 feet of gas, specific gravity 560. 



In the Hydrodynamie of Bossuet, he states as the result of experi- 

 ment, that an aperture of one inch in diameter, under the pressure of 

 a column of water 10 feet in height, discharged 8,574 cubic inches, or 

 4*96 cubic feet of water per minute. 



By an experiment made at the Leith Gas Works, a hole, one inch 

 in diameter, under the pressure of one vertical inch of water, dis- 

 charged 17*7 cubic feet of gas, specific gravity 560, in the same time. 



Now, comparing these discharges by the square roots of their 

 respective impelling columns, we have 



Water, Gas, 



^ 10 feet : 496 : : >/ 122 feet 17.33, 



instead of as above, the actual discharge 17-70. 



Again, Bossuet reports, that a hole 2 inches in diameter, with a 

 pressure of 11 feet 8 inches and ten lines of water, discharged 13,021 

 cubic inches of water in 21 seconds, or at the rate of 25*52 cubic feet 

 per minute. 



It was also found at Leith, that a hole 2 inches in diameter, with a 

 pressure of one inch of water discharged 69*5 cubic feet of gas, spe- 

 cific gravity 560, per minute. 



Reducing the fractions of Bossuet's pressure to decimals of a foot, 



