206 
FIELD RANGE-FINDING. 
wind. Long tapes break, and require frequent renovation of gra¬ 
duations and figures, when used on rough ground in wet weather. 
Lines or wires are better, but are awkward to wind up, and if provided 
with numerous tallies for graduations become cumbrous and heavy. 
Constant bases 50 or 100 yds. cannot always be obtained, and even 
when they can, the view of the object or the other end of the base 
may be obstructed by buildings, trees, &c., or troops. Instruments 
containing their own base 1 yd. long or otherwise may become bent. 
Men 6 ft. high in the enemy's ranks sometimes decline to stand at 
attention while observations are being made on them. On the whole, 
perhaps a moderately long base, measured by means of a short 
auxiliary base, is the best for military purposes. 
The effect of a given error in measuring the base increases with the 
range, unless the base increases in the same proportion as the range. 
An error of 1 yd. in a base of 100 yds. causes an error of about 20 yds, 
at 2000 yds. range. 
(3) Calculation is of course inadmissible in the field, and the mode 
of getting over this difficulty has generally been the chief characteristic 
of different inventors' ideas on range-finding. There are literally 
hundreds of ways of doing it, none of them possessing any very 
marked advantage over the other; but all, or nearly all, effect their 
object. Some are more accurate and admit of closer reading than 
others; but in this, as in everything else, the simplest plan is the best 
for military purposes. 
The fewer distinct operations in finding a range the better, so we 
may discard at once separate pieces of apparatus such as Nolan's 
calculating roller, or books of tables. Pencils are apt to lose their 
points or get lost themselves on service, so the plotting system may 
share the same fate (Edwards', class I.) 
Micrometer screws and vernier scales are likely to be read hurriedly 
when bullets are flying about; so practically we are reduced to the 
method by which the range in yards is read direct from a tape, and it is 
difficult to see how any other plan can compete with such a simple device. 
Briefly, if accuracy is to be attained in measuring the range, we 
must have accuracy somewhere in the observations and measurements; 
and it is much better to leave accuracy of adjustment of instruments to 
the manufacturers, whose business it is, than to do it ourselves. This 
is accomplished by using an angle-finder fixed at a constant angle. 
If all necessary calculation can be done for us by actuaries or Babbage's 
calculating machine, and the results printed in a line, one below the 
other, on a tape, why not let it be so, instead of injuring our eyes by 
reading verniers ? Here it may be remarked that it would be highly 
desirable, for more reasons than one, that only one man should be 
required in finding a range; but as this generally involves some 
sacrifice of speed, we shall probably have to content ourselves with 
a system which admits of working by one man alone on an emergency. 
In selecting a system of range-finding, all we have to do really is to 
choose between intricate and simple, and fix our standards of sim¬ 
plicity and accuracy, which latter might be from 1 to 2 per cent, of 
range. Lastly, if experts—specially selected and carefully trained 
