Mr. MaoKain on the Compression of Water. 251 



tion to tho limit of rigidity of the materials used in experimental 

 apparatus, that there is much room for doubt, as to whether or not the 

 indications heretofore recorded, bo not compound measures of the 

 elasticity of water, and of the materials of which the instruments have 

 been formed. 



It has occurred to mo, that if the results of experiments were noted, 

 in which great bulks of water were employed, but operated upon by 

 slight forces, that a degree of compression might be ascertained, suf- 

 ficient to remove much of tho doubt that may at present be entertained 

 as to the rigid accuracy of the experiments on which our ideas of the 

 elasticity of water are at present based — further, that, in these experi- 

 ments, should any analogy be discovered between the ascertained laws 

 which govern the compression of air, and the comparative indications 

 of compression of water — we may take the laws which repeated ex- 

 periments have proved to govern the compression of air, as analogous 

 rules for the compression of water ; and, calculating from them, may 

 compare the theoretical results which the laws would furnish, with 

 similar conditions ascertained by experiment. 



Following out this idea, it appears probable that the transmission 

 of water and gas through long ranges of pipes, may, by the compara- 

 tive forces required to propel given quantities through them, give an 

 approximate rule for estimating their compressibility — for, if water 

 were totally incompressible, there would undoubtedly be some differ- 

 ence between the quantities of air or gas transmitted through a pipe, 

 and that of water by a corresponding force, through a similar pipe — 

 the one would accumulate in density according to the force required 

 for its propulsion ; while the movement of the other would be like a 

 bar of iron, influenced only by friction. 



In the transmission of water through long ranges of pipes, it has 

 been ascertained that the quantity discharged by a pipe of any given 

 diameter and length, is inversely in proportion to the square root of 

 the length — and directly proportional to the square root of the height 

 of the column of water employed to propel it. 



The comparatively recent adaptation of carburetted hydrogen gas, 

 for the purpose of lighting towns, has required attention to the laws 

 by which it is conveyed through pipes. Gas is usually forced through 

 pipes, by employing a slight column of water, of a height sufficient to 

 propel the required volume with the velocity required. Now, as 

 already mentioned, the laws of compression of gases and air have been 

 exactly ascertained; and it is thence evident, that even the slight com- 

 pressing force usually employed for the transmission of gas, must pro- 

 duce an alteration in its bulk, at the place where the motion originates. 

 The most exact observations made as to the laws by which gas is 

 conveyed through pipes, show that in like manner as water, the 

 quantity which a pipe can discharge, is inversely proportional to the 

 square root of the length of the pipe, and directly proportional to the 



