1922.J 
Jenkinson.—Development of the Locomotive. 
295 
this since it is a fairly simple problem to solve approximately. Train- 
resistance formulae are in everyday use, and are checked in practical 
working constantly, so that the force necessary to maintain any train at a 
certain speed on the level is closely known. Taking, then, the average 
running-speed of any train from terminal to terminal, the average horse¬ 
power is easily arrived at by using the well-known formula— 
TT Train-resistance in pounds X speed in miles per hour 
Horse-power = - - --- - - 
o / o 
adding, of course, the necessary correction for any difference in level. 
One of the best performances ever recorded on the 3 ft. 6 in. gauge was 
accomplished by the New Zealand Ab class locomotive on the 29th January, 
1916, when a load of 423 tons behind the tender was hauled from Timaru 
to Christchurch at an average running-speed of forty-six miles per hour. 
This represents work being done at the average rate of 637 horse-power ; 
but during that part of the journey from Temuka to Rangitata, this was 
largely exceeded, over 1,000 horse-power being maintained. The coal 
burnt was not accurately measured, but was certainly less than 2 lb. per 
brake-horsepower-hour. On several occasions I have observed the same 
boiler working at the rate of over 800 h.p. without being seriously pushed, 
and on one occasion this was being done at the slow speed of fourteen miles 
per hour. In all these calculations wind-pressure has been neglected; and, 
taking all factors into consideration, there is no doubt whatever that this 
boiler can develop 1,200 h.p. comfortably. It will be hardly credited that 
this power is developed from 1,500 sq. ft. of heating-surface, and 35 sq. ft. 
of grate-area, and from a boiler weighing 15 tons, with all fittings, and that 
the pre-war cost of the same was about £900, or 15s. per horse-power. These 
figures will probably .stagger those conversant with boiler powers and costs 
generally, but represent fairly what can be expected from a well-designed 
modern locomotive-boiler with a superheater and large fire-box. 
The fuel-efficiency of these boilers is extraordinarily high when working 
steadily at low blast-pressure, and here I am able to quote the official figures 
of a test extending over ten trips between Christchurch and Timaru 
(Table I). The loads hauled were small, but the weather was variable, 
and, as before, wind-pressure has been neglected. All water and coal was 
carefully measured, and the figures include all stand-by losses, both on the 
road and in the shed. Actually 9 lb. of water was evaporated for each 
pound of coal burnt, but, remembering that the working-pressure was 
1801b. per square inch, and that the average steam-temperature was 
620° F., it is clear that the equivalent evaporation was 11-96 lb. from and 
at 212° F.; or, allowing 10 per cent, for steam used in air-pumps, lubri¬ 
cators, &c., without superheat, 11,550 B.Th.U. were usefully given to the 
boiler by each pound of coal burnt. The work done in actual haulage at 
the average speed of thirty-five miles per hour would amount to 7,360 brake- 
horsepower-hours ; but there are other factors to consider. Strong north¬ 
west gales were blowing on two days, the average speed was often greatly 
exceeded, there was a fair amount of light running at terminals, and a con¬ 
siderable amount of work done in braking and accelerating the train. No 
experienced railway engineer will dispute that this amounts to at least 
20 per cent, extra work, so that quite 9,000 brake-horsepower-hours were 
done. The total coal burnt was 27,000 lb., so that it took 3 lb. of coal to 
generate each brake-horsepower-hour of useful work, including all stand-by 
losses. 
