AUTO-SIGHTS. 
441 
NOTE BY MAJOR H. C. DUNLOP, R.A. 
Professoryf Artillery at the Ordnance College. 
If E denotes the error due to laying or that in the level of the racers, 
Professor Greenhills first formula becomes 
(1). aR ipEB 
R ~ (M±E) (B + M) 
At long ranges where B is large as compared with M it becomes 
(2.) aR _ hF E 
TT ~ M ± E 
which is the formula for a depression range finder or position finder 
out of level or badly laid. 
Again if p is the percentage too low or too high of the setting of the 
tide lever, and if there is no error in the racers or laying, the formula 
becomes 
(3) . AR ±pMB _ + p B 
R = {M (100 ±p)}(B + M) “ (100±p)(B+M) 
At long ranges where B is large as compared with M this becomes 
(4) . AR = + P 
R 100 ± p 
which is the formula for a Position Finder or Depression Range Find¬ 
er with a similar error in the setting of the height. 
Now formulae ( 2 ) and ( 4 ) are always greater than formulae ( 1 ) and 
( 3 ). In other words such errors as we have considered affect a posi¬ 
tion finder or depression range finder more than an auto-sight. It 
is well known that they affect ordinary laying less. But we must re¬ 
member that an auto-sight combines range finding and laying, so that, 
when considering its errors, we must compare them with all the errors 
resulting from the combined use or a depression range finder and the 
ordinary laying appliance. There are then so many errors and so 
many corrections and sometimes so many cooks that it is doubtful if 
there can be any satisfactory test except hits at practice. It is quite 
certain that, though in helping to trace the causes of misses they have 
their uses, formulae and figures can prove anything except the proba¬ 
bility of the assumptions or the reliability of the statistics on which 
they are based. We require an enormous mass of such circumstantial 
evidence before we can hope even to approach the truth, but direct 
hits are direct evidence and credible. 
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