1822.] with Remarks on the Apparatus. 277 



resistances from 90 to 30 degrees. At this angle the numbers 

 are nearly equal, the resistance being rather greater ; afterwards 

 the sines again exceed the resistances. This comparison might 

 have been more readily made by dividing all the resistances by 

 the greatest resistance, and under these ratios placing the natural 

 sines which are to be found in many books of logarithms. 

 These numbers and their squares are also inserted, and in no 

 one instance do the experimented resistances coincide with the 

 square of the sine. The reduced direct resistance when com- 

 pared with the plane's resistance at six feet in a second, see 

 Table IT. is in excess 2-1- pounds. This discrepance may be 

 partly attributed to the larger surface of the two planes, and 

 partly to subsequent improvements of the apparatus with which 

 the experiments of Table II. were made. A motive weight of 

 42,885 pounds, according to the experiments in that table, would 

 produce a velocity of 6,587 feet per second. 



Two circumstances affecting the obhque resistance are the 

 negative pressure and the accumulation of the fluid on that part 

 of the plane on which it first strikes ; that such an accumulation 

 takes place is well known to practical men from the greater 

 stress of the weather brace above the lee one of square sails 

 hoisted by the middle, and forming an acute angle with the 

 wind's direction. This fact is exempUfied in the custom of 

 slinging the yards of luggers by the thirds, by which one-third 

 of the yard is before, and two-thirds behind the mast, and an 

 equilibrium of the pressure of the wind is produced. That non- 

 elastic fluids produce a similar effect was clearly shown in the 

 rudder of the vessel built under the inspection of the Idte Earl 

 Stanhope. His lordship, with the view of lessening, or rather 

 annihilating, the labour of the helmsman, caused the pivots of 

 the rudder to be inserted in the middle of the upper and lower 

 surface, but on trial to produce the desired equipoise, it became 

 necessary to shift the axis a third of the rudder's length, reckon- 

 ing from the foremost extremity. From these observations, it 

 appears that the oblique resistance of a plane consists of four 

 parts, the impulse, the friction, the minus pressure, and an accu- 

 mulation of the fluid on the fore part of the inclined surface. 

 That these experiments are superior to any yet pubhshed may 

 be inferred, without arrogating any great merit to those who 

 made them, from the size of the experimented bodies, and to the 

 accuracy of the apparatus which measured the velocity of the 

 moving bodies to a small fraction of a second, a circumstance 

 essentially necessary to obtain accurate results. It is most 

 desirable that experiments of this kind should be repeated ; and 

 I anticipate with much pleasure the pubhshing of the second 

 volume of Hydrauhc Experiments made at Fahie Mines, in 

 Sweden, under the scientific and able management of Messrs. 

 Lagerhjelni and Kails tenius, at the cxpence of the Mineral 

 Society. 



