696 Report of the Consulting Engineers on the Trials of 
ing as the motion during each revolution was irregular or 
was steady. The tachometers were very useful to the drivers 
in indicating a rise or fall in speed, and the Judges were by 
their aid able to form precise opinions on the merits of the 
governors and on the conditions of balance of the engines. 
During the trials a question was raised by some of the 
spectators as to the additional load thrown on the brakes by 
the water pouring on them to keep them cool. It was argued 
that setting the water into motion and flinging it off at a 
high velocity would absorb an appreciable amount of power. 
The value of this objection, in the worst case, is easily 
calculated. 
Supposing the whole of the water flung off at the full velocity 
of the periphery of the brake-wheel (which is 17 feet in circum- 
ference), at 150 revolutions per minute, then each pound of 
water would have a velocity of 42 ' 5 feet a second communicated 
to it, and its energy would be g^— j- =28 foot-pounds. The 
actual flow of water was 4*4 lbs. per minute, so that the 
additional work thrown on the brake was 123 foot-pounds 
per minute, and as the load circle ran 2595 feet per minute, 
it follows that the additional load in the scale-pan would be 
123 foot-lbs. lu 1 
— — : = '047 lbs., or 4 oz. 
2d95 leet ^ 
But the greater part of the water fell off without attaining 
any considerable velocity, so that it may safely be said that the 
water used in cooling the brakes did not add any appreciable 
load to the engines. 
In order to facilitate comparison with the trials made at 
Cardiff in 1872, the brake horse-power has been worked out 
without the corrections for friction as well as with it. The 
figures originally given on the trial ground at Newcastle are not 
quite correct, the resistance of friction having been estimated 
too highly, but no error arose as to the comparative results, 
because ail the brakes were subject to the same degree of error. 
The fuel consumed per brake horse-power has also been cal- 
culated with and without correction for brake-friction,' and, in 
addition, in order to make the results comparable with Cardiff, 
a correction has been introduced for the slightly superior 
quality of the Powell's Duffryn coal used. The Llangennech 
coal hitherto employed in the Society's trials was determined by 
!Mr. Snelus in 1871 to have a calorific value of 14,718 units per 
1 lb. Mr. Stead (see Table VII., page 727) has calculated the 
value of the coal used at Newcastle at 14,940 units per 1 lb., 
or about 1^ per cent, higher, so that the coal consumption at 
Newcastle must be multiplied by 1*015 to make it comparable 
