MR. RENNIE ON THE FRICTION AND RESISTANCE OF FLUIDS. 427 
experiments on the subject* : whatever has been effected by our engineers or 
scientific men, has either been withheld from the public, or consigned to ob- 
scurity ; and though we have tracts of marshes and fen land, consisting of 
many thousand acres, the dissertations on the mode of draining and carrying 
off their superfluous waters are confined to local pamphlets and reports, of com- 
paratively minor interest to the science of hydraulics. 
From the foregoing short but imperfect history, it is obvious that much has 
been done towards perfecting this science. It is however certain, that much 
yet remains to be accomplished ; and although we are deeply indebted to both 
the French and English philosophers for their extensive investigations on the 
laws of capillary attraction, the descents of globes in fluids, and the adhesion 
of fluids to metal discs, the phenomena of fluidity, and the laws which govern 
the motion and equilibrium of their particles, must yet remain a problem 
purely geometrical; and as we possess no tangible means of approximating to 
the solution of the problem, but through the intervention of a solid, we must 
content ourselves, in like manner, with the imperfect formulae deduced from 
experiments made on a small scale on the friction and adhesion of water in 
pipes and conduits, until we can ascertain more correctly the causes of the 
retardations of rivers as they occur in nature. 
In the consideration of this question, therefore, I propose to examine, first, 
the retardations of the surfaces of solids moving in fluids at rest ; secondly, 
the retardations of fluids over solids; and, thirdly, the direct resistance of solids 
revolving in fluids at rest. 
To illustrate the first case, I caused an apparatus to be constructed, of 
which the annexed Plate XI. is a representation ; it consists simply of a 
cylinder of wood ten inches and three quarters in diameter, and twenty-four 
inches long, and divided into eight sections of three inches in each, and fixed 
upon a spindle of iron about four feet in length, and one inch and a quarter 
thick. The apparatus was accurately turned and polished. Upon the upper 
part of the spindle, a small cylinder or pulley, six inches in diameter was fixed, 
and a fine flexible silken cord, communicating with the weight, was wound ; 
* The experiments of the Society for the Improvement of Naval Architecture, in the years 1793, 1794 
1795, 1796, 1797, 1798, relate principally to the resistances of solids moving through fluids. 
