298 The N.Z. Journal of Science and Technology. [Jan. 
But this was on a very favourable line, where the engine was doing 
steady collar work during the whole running-period. Different conditions 
exist between Wellington and Taihape, where steep, alternating grades and 
sharp curves are common. On this run also we have the records of a 
week’s trial to guide us (Table II), and we find that the boiler-efficiency falls 
15 per cent, and the cylinder-efficiency about 15 per cent, when compared 
with the more favourable southern run. In other words, nearly 4 lb. of 
coal are required to generate a brake-horsepower-hour. Under the most 
unfavourable conditions, such, for instance, as exist on the Rimutaka 
Incline, were an ordinary locomotive used for that run, a brake-horsepower- 
hour is generated by 8 lb. of coal. 
So far as I know, such figures have not been worked out before, certainly 
not with so much data to draw upon and as the result of actual working- 
trials. They deserve the honour of a recapitulation.' A modern super¬ 
heated steam-locomotive will— 
(1.) Generate a brake-horsepower-hour when working steadily at a power 
well within its capacity on 2 lb. of coal (28,000 B.Th.U.) ; 
(2.) Generate a brake-horsepower-hour working over favourable country 
with grades less than 1 in 100 in ordinary working, and including 
all stand-by losses, on 3 lb. of coal (42,000 B.Th.U.) ; 
(3.) Generate a brake-horsepower-hour working over unfavourable 
country with alternating grades as steep as 1 in 50 in ordinary 
working, and including all stand-by losses, on 4 lb. of coal 
(56,000 B.Th.U.). 
We can now proceed to a comparison between steam and electric 
working. The great defect of electric locomotives is the small amount 
of power generated per unit of weight, and this is especially noticeable 
where the motors are fitted between the wheels on the 3 ft. 6 in. (or 
narrower) gauge. So far no electric locomotive generates more than 15 h.p. 
per ton weight, and the majority fall below this. This is not so important 
on long runs at high speeds over level country, where the steam-loco¬ 
motive is handicapped by the heavy weights of coal and water carried in 
the tender, though even here the electric locomotive must be heavier for 
the same work ; but on short hilly sections it becomes a serious drawback. 
The limit of power for the electric locomotive on the 3 ft. 6 in. gauge is 
160 h.p. per axle, and with 12-ton axle-loads this works out at under 
14 h.p. per ton. On short sections such as Otira Tunnel a suitable steam- 
tank locomotive would give 20 h.p. per ton, and this is one of the reasons 
why electrification gives such poor results on this class of line, and why 
it will cost over three times as much to work the Otira Tunnel with 
electricity as with steam. I feel confident, however, that better results 
can be attained with electric locomotives, and will be when the experience 
of locomotive engineers is made use of in their design. The present method 
of fitting the motors between the wheels must be abandoned, and, when 
they are placed in the body of the vehicle, room will be available for more 
powerful motors, and a higher centre of gravity (which is very desirable) 
will be attained. In the ensuing comparisons I will assume that a more 
efficient electric locomotive has been designed, giving 15-20 h.p. per 
ton even on the 3 ft. 6 in. gauge. The next point is to decide on some 
standard of prices. I propose to compute all costs and charges on a basis 
50 per cent, above pre-war rates of 1914, and interest will therefore be 
rated at 6 per cent. Taking a life of twenty-five years for the locomotives 
and thirty-five years for the plant, depreciation works out at 3 per cent. 
