Porlalle Agricultural Steam Engines at Newcastle. 695 
No. 1 brake with its tachometer was placed in an elevated 
position, a pullev 36-2 ioch in circumference was keyed on to 
the shaft in lieu of the coupling, a cord was wound round the 
pulley, and the brake was caused to revolve by means of 
weights hung on till a load was found under which steady 
motion was maintained. In this way it was ascertained that, 
after a preliminary push or start was given to the wheel, 13 lbs. 
produced a decided acceleration, while 12 lbs. were incompetent 
to keep the wheel turning : hence, the resistance of friction was 
about 12 J lbs. acting on a pulley 37 inches circumference to 
the centre of the cord. The weight revolving was 756 lbs., the 
total weight was, therefore, 756 lbs. -f the 12^ = 768^ lbs. The 
journals of the brake shaft are 2^ inches diameter, consequently 
the coefficient of friction comes out •0766, which is about the 
usual figure accepted for the friction of shafts. 
The circumference of the circle in which the point of attach- 
ment of the brake-load occurs is 17 "3 feet, subject to trifling 
variation arising from the wear of the blocks, which variation 
is apparent in Table IV. (p. 725). The weight of No. 1 brake- 
wheel, shaft, strap, and coupling shaft, is 946 lbs., so that the 
weight corresponding to the friction of the apparatus, if placed 
in the scale-pan, would be, 
12 "5 lbs. X 37 inch x 946 lbs. t i. ' " 
= = 2" <4 lbs., 
17-3 feet x 12 inch x 76S-5 1bs, 
being in round numbers '003 of the weight of the revolving 
parts and brake-strap. The scale-pan weighs 8i lbs., which is 
increased to 8 "525 lbs. when the friction due to its weight is 
added to it, and 946 lbs. X '003 = 2- 838 lbs. friction due to 
the whole weight of the brake, making 11-363 lbs. of perma- 
nent load at the scale-pan. Calling the load to be placed ia 
the scale-pan W, its effective weight, adding friction, will be 
1*003 W. Then if C be the circumference of the circle to 
which the weight hangs, and R the number of revolutions 
per minute, the brake horse-power of ?so. 1 brake will be 
_ (1-003 W + 11-363) X C X R 
33000 
The other two brakes have corresponding formulae, differing 
only in the constant 11-363, on account of the different weights 
oi the various parts. 
An addition of considerable value was made by fitting the 
brakes with Thome's electrical speed-indicators or " Tacho- 
meters." These instruments indicated on a large graduated 
dial, not only the speed at which the engines were running 
at any moment, but also the variations of speed during each 
revolution, the index-hand oscillating more or less accord- 
