304 
PROFESSOR 0, REYNOLDS AND MR. W. H. MOORBY 
load with the lever horizontal, and a constant moment of resistance maintained what¬ 
ever may be the speed of the engines. 
(3.) Manchester town’s water, of a purity expressed by not more than 3 grams of 
salts in a gallon, brought into the laboratory in a 4-inch main at town’s pressure (50 
to 100 feet), and distributed either direct from the main or at constant pressure from 
a service tank 10 feet above the floor of the laboratory. 
(4.) Two tanks, each capable of holding 60 tons of water, one in the tower, 116 feet 
above the floor, the other 15 feet below the floor, connected by 4-inch risino- and 
falling mains, each 500 feet long, passing in a chase under the floor. The rising 
main including a special quadruple centrifugal pump, 2 feet above the floor, ca 23 able 
of raising a ton a minute from the lower to the upper tank. (Shown in Plate 7.) 
Also a set of mercury balances, showing continually the levels of water in the two 
tanks, and the pressures in the rising, falling, and towns mains. (Shown in Plate 4.) 
(5.) A special quadruple vortex turbine, supplied from the falling main and dis¬ 
charging into the lower tank, capable of exerting 1 h.p., and available for steady 
speed at all parts of the laboratory. (Shown in Plate 7.) 
(6.) A supply of power to the laboratory by an engine and boiler, quite distinct 
from the experimental engine, and distributed by convenient shafting which is 
always running. (Shown in Plate 3.) 
The Measurement of the Worh. 
4. Of the apjDliances mentioned, the brake on the low-pressure engine is the 
centre of interest, as it was by this that the work wms measured, as well as con¬ 
verted into heat. 
The existence of the appliances was largely due to the interest in educational work 
taken by Mr. William Mather, who, together with the other members of the Arm 
of Mather and Platt, not only placed at my disposal the facilities of their works, but 
inspired the enthusiasm which alone rendered the execution of such novel and special 
Avork possible. 
The development of the brake dynamometer, from its introduction by Prony, has 
an interesting and important history, but into this it is not necessary to enter. 
The purpose of these dynamometers is to aftbrd continuous frictionai resistance 
adapted to the power exerted by the prime mover in causing a shaft to revolve, and 
of a kind that is definitely measurable. To fulfil the first of these conditions, the 
mean moment of resistance of the brake must just balance the mean moment of eftbrt 
of the engine, and the means ol esca^ie of heat from the brake must be sufficient to 
allow all the heat generated to depart without accumulating to an extent which mav 
interfere with the action of the appliances. In the first brakes the resistance was 
obtained by the friction of blocks or straps pressed against a cylindrical wheel on the 
shaft, and, small powers being used, radiation and air-curi’ents round the brake Avere 
