506 
MINUTES OF PEOCEEDINGS OF 
6 inch plan. In order truly to depict the incline a in this case, the contours 
should be run at a vertical interval of 100 feet, and we shall thus obtain a 
horizontal equivalent equal to the base AB on the 6 inch scale—viz. AB in 
the figure. 
By a simple proportion, the vertical interval at which the contours should 
be run can easily be ascertained. Bor example, supposing we are making a 
military sketch on a scale of 30 inches to the mile, we should have— 
in. in. ft. 
30 : 6 :: 50 
= 10ft. vertical interval; 
the scale of shade can then be applied to the plan of these 10 feet contours. 
When the sketcher is in possession of a plan on the 6 inches to the mile 
scale, and contours with a vertical interval of 100 feet given, and is desirous 
of shading the plan, it will be necessary to interpolate a contour half way 
between those given; the scale of shade can then be applied, and the 
inclines will then be shaded in accordance with it. If, on the other hand, 
the plan shewed contours with a vertical interval of 25 feet, it would be 
necessary to apply the scale of shade between every second contour. Again, 
if the scale of the plan.was other than 6 inches to the mile (say 30 inches), 
and the contours given were of a vertical interval of 20 feet, it would be 
necessary to interpolate a contour in this case before applying the scale of 
shade, as the vertical interval for a scale of 30 inches to the mile should be 
10 feet. 
The opinions as regards the advantage of using a scale of shade, appear 
to be very various; some are strongly in favour of it, and others, on the 
other hand, are very much averse to it. I believe it is of great use for 
instructionalpurposes ; for it convinces a draughtsman that, by means of his 
pen or pencil, he can obtain at least nine different shades—whereas a 
draughtsman who has not practised with it is apt to restrict himself to two 
or three, and consequently represents only two or three inclinations of 
ground. But when a good draughtsman has done five or six careful drawings 
with it, and thus learnt the handwriting , he can afford to trust to memory 
for shading his drawing, and only use the scale of shade to check his w r ork 
occasionally ; for he will find by adhering strictly to the rules laid down for 
its use, they will rather cramp him than otherwise—whereas a bad draughts¬ 
man, to obtain anything like accuracy, will have to go through the laborious 
process of using it mathematically. The latter may be compared to a man 
who, having to cross a number of w^et ditches, and knowing he cannot jump 
them, sees the advisability of carrying a plank with him to act as a bridge; 
the former, having to cross the same ditches, and knowing he can jump 
them, will find the process of carrying a plank with him rather an impedi¬ 
ment than otherwise. 
The fact of getting a number of draughtsmen to shade an inclination by 
the same amount of shade, is certainly a great advantage; for eight or ten 
men's work can be put together, and form a tolerably harmonious whole. 
The handwriting of the scale of shade is, perhaps, rather too course; for 
when a shade has to be made up of a number of strokes, if these strokes are 
placed beyond a certain distance apart, the eye will begin to count units, and 
consequently lose the idea of shade. 
