LIGHT RAILWAYS FOR NEW SOUTH WALES. 225 
it is possible to draw between the two curves, and cuts the grade 
line at one hundred and five feet per mile, or a ruling grade of, 
say, one in fifty. This solution, which he believed was due to 
Mr. W. H. Searles, assumed that trains could always be fully 
loaded, and referred only to goods traffic, but the number of 
goods trains was generally a fair indication of the number of 
passenger trains ; if not, the correction could be made. Should 
the tonnage “up and down” differ greatly in amount, the branch 
or section must be considered as two lines, A to B, and B to A, 
and graded accordingly. Closely allied to fixing the ruling grade 
-came grading in general, or location in elevation as it might be 
termed. The first cost could often be reduced without affecting 
working expenses by the adoption of momentum grades. Since 
an initial velocity of twenty-five miles per hour would lift a train 
through a height of twenty-two feet before bringing it to rest, 
wherever in ordinary working such a velocity could be relied on 
it was possible to introduce a hump in the ordinary grading to 
this extent, and thus often materially reduce cuttings. Sags to 
the extent of nearly twenty feet might also be introduced in the 
banks, since the velocity gained in descending served to carry the 
train over the corresponding rise. The switch-back formed a good 
illustration of momentum grading. Such grading was particularly 
applicable to undulating country, as some portions of the Western 
Plains. On the question of gauge, he fully agreed with the author 
that the narrow gauge per se reduced the first cost by only a small 
percentage, about five per cent., according to Mr. Wellington. 
The great reduction in first cost in the case of narrow gauge lines 
generally arose from the fact that sharp curves were adopted, but 
curves almost if not quite as sharp might be used on the standard 
gauge. As pointed out by the author, the question generally was 
not simply the standard versus the narrow gauge, but the standard 
versus a break of gauge. 
Mr. G. R. Cowprry agreed with the author with regard to 
_ the gauge and curves, but was, however, of opinion that it was 
undesirable to depart from the minimum grade even where it 
O—July 5, 1893. 
