710 PHILOSOPHICAL TRANSACTIONS. [aNNO 17t)3. 



In order to examine the quantities of friction proceeding from different weights, 

 Mr. F. had an exact balance made, which weighed 27 oz. ; the pivots of the 

 axis were 4- inch diameter, and turned in brass sockets, fixed in a frame for the 

 purpose. At each end of the beam he suspended several pairs of equal weights, 

 and then tried how much added at one end would just move the beam, and also 

 how much would depress the end 2 inches. Whence he infers, that the least 

 power required was equal to -f the weight on the pivots ; and that it required a 

 power nearly equal to the whole weight, to overcome the resistance from friction 

 with but a small degree of velocity. 



It is not imagined that these experiments should determine the exact quantity 

 of friction proceeding generally from weight or pressure : which probably can 

 never be ascertained by any experiments, however accurate ; for even in engines 

 of equal dimensions, and loaded with equal weights, the quantities of friction 

 may be very unequal, from circumstances differing, which are sometimes imper- 

 ceptible ; such as the firmness, elasticity, roundness and smoothness of the parts 

 rubbing on. each other ; particularly the roundness, and smoothness of the gud- 

 geons or pivots, which in large engines are seldom turned true, or polished. 

 But it appears from these experiments, that the quantity of friction in large en- 

 gines may reasonably be estimated at 4 the weight, or pressure, on the rubbing 

 parts ; though in such as are small, and finished with exactness, the quantity 

 may probably be about 4-. 



Mr. F. then endeavours to determine how much friction will be lessened by 

 placing the axis of a wheel on the circumferences of two other, or friction wheels ; 

 and also the pivots of these two each on two others, &c.; calculating the dimi- 

 nution of the friction on the ratio of the decrease of velocity in each wheel or axis; 

 hence he says, thus it is evident that by the application of additional wheels, or 

 by enlarging the diameters of these, the resistance from friction may be reduced 

 to less than the resistance of the medium the wheel passes through. 



In order to form some estimate of the quantity of weight with which the axis 

 of the lever of a fire-engine is loaded, Mr. F. took the dimensions of the several 

 parts of that at the York -buildings water-works; the lever of which is 27 feet 

 long, 2 feet 6 inches by 2 feet 2 inches in the middle, and 2 feet by 22 inches 

 at the ends. The weight of which, with the archeads, chain, rods, and work- 

 ing frame hanging at one end, and the piston and chain at the other, may be 

 computed at 6 tons, or 12,000 lb. The cylinder is 46 inches diameter, about 

 1591 square inches; which at 15 lb. per inch pressure of the atmosphere, is 

 22,274 lb. The column of water to be raised is 10,o6olb., which is not 64 lb. 

 per inch; so that the remainder of the power is employed in overcoming the 

 resistance from friction in the several parts of the engine, and giving the lever 

 a degree of velocity equal to 120 feet per minute, which it moved in common 

 work. 



