The record-union., 1898-03-03
HOW BIG GUNS ARE AIMED.
The Range-Finder Used ON Sea-
coast Defenses and Batt1eships.

In reply to an inquiry from James
Thompson of Chicago / would say that
the range-finder used on our seacoaSt
defences is not a Government secret,
but is patented appliance, an improve
ment upon a system that has been in
use since ancient times. There are in
use three sets of apparatus somewhat
different from each other, which We're
| invented by Captain Watkins, an Eng
/ lish engineer; Lieutenant Fisk of our
navy They are very complicated, and it
is difficult to explain their operation so
/ 1T can be understood by laymen. All
such inventions are an appliance of the
mathematical principle that, knowing
the base of a triangle and the two angles
at its eXtremities, one can calculate the
distance between them. On coast de-
fences the base of the triangle is perma-
nent, with fixed objects to mark its
terminus. The angles are ascertained
by observations through instruments
made for that purpose, and when they
are known there is a series of printed
calculations covering all possible situa-
lions which enables the gunner to catch
the distance Of his target at a glance.
| AT sea, When a vessel is moving, the
| base is fixed and measured upon the
deck. A telescope is placed at either end
of that line, and the lenses of both are
focused upon the object to be shot at.
| An observation is then taken, rapid
| mathematical calculation is made, the
| book of tables is referred to, and in a
moment the gunner may know whether
| the enemy's cruiser is five and half
or six and one-fourth miles away, or
any other given distance This of
course. requires a great deal of. techni-
cal skill and mathematical ability, but
it is said to be absolutely accurate, and
the apparatus is so sensitive and regu-
lated to such fine degree that by turn
| ing key monster gun weighing a hum
dred tons con be instantly adjusted so
that with given quantity of powder it
will carry a projectile of a given
| weight exactly the distance
which the range-fnder has de-
termined. OF course, the gunner must
know the contents of his cartridge, be-
cause that is a material factor in his
problem. He must also make allow
ances for the wind, for the resistance of
the atmosphere, for the curvature OF
tbs earth and for the movement of the
enemys fleet if it is in motion. The
range-finder is, however, a great deal
more accurate than the human eye, and
persons with defective vision will often
insist that gun is badly aimed and
find out to the contrary after the shot is
| fired.
| Although we have guns on our battle
ships and in the fortresses on the coast
| that will carry projectile thirteen miles
| it would be folly to attempt to use
them at that distance because
owing to the curvature of the
earth. it would be impossible
to see the target. A man in a small boat
upon the surface of the water cannot
see more than four miles. From the
bridge of an ordinary man-of-war,
which may be thirty feet from the water,
a man with good eyesight or with a
glass can see eight or nine miles. A
man at the masthead can see ten or
twelve miles, but very indistinctly, and
that is the limit of human vision on a
level surface.-W. E. Curtis in Chicago
Record.