Harrisburg telegraph. [volume] (Harrisburg, Pa.) 1879-1948, 1919-10-27
VOW a little piece of platinum,
\ electrically heated, placed on

M electrically heated, placed on
the top of an empty kerosene
can and wired up with other ap-
paratus, far in the rear, located Ger
man guns and helped win the war
was explained to the members of
the Franklin Institute by Prof.
Augustus Trowbridge, of Princeton
University.
Doctor Trowbridge has charge of
a corps of men who did excellent
work in the American expeditionary
force in sound and flash ranging
work for artillery firing. He has
been decorated with the d. s. NJ,
the ID. S. o. and awarded the Legion
of Honor by France for his snare in
directing these men.
In the former days of warfare
artillery was not used to such an ex-
tent as to make this branch of the
service necessary, but with the in
crease in size and number of can
non it was found that means other
than actual observation were needed
to locate enemy batteries. Prof.
Trowbridge, who holds the chair of
physics at Princeton, offered his serv-
ices to the Government, and was
placed in charge of this new work.
Need For Method Seen
1.-The need for some method of
spotting enemy batteries was evil
dent soon after the outbreak of the
war" he said, land it was found
that my observing enemy guns from
different stations and reporting to a
central bureau that the positions
could be quickly plotted.
For, instance, if we have three
observers watching the enemy lines
oh 10 NJ oh
sees the flash or smoke of the enemy,
they can easily with instruments get
the angle from north of that object.
This is Immediately telephoned to
central station. There, there is a
large plotting board and map with
the observation posts clearly mark
ed Then by following the lines of
sight reported, the intersections of
the three lines will pretty closely
mark the location desired.
This system was found very ex-
cellent for good weather. but i'll rain
and fog was absolutely impossible.
1t was then found possible by means
of scientific machinery to locate the
guns by means of the sound. This
took a delicate and complicated bit
of machinery. The important work
was done by small bit of platinum
wire heated by electricity and con-
nected with other apparatus which
would record all changes in tenn
perature.
This change of temperature
would take place when the vibra-
tion, caused by the noise of the shell
as it broke the air in passage, and
the sound of the gun, forced fresh
air against the bit of wire. Six such
instruments would be set up along
an arc equidistant from the sus-
pected area.
"In addition, there would be OBJ
servation posts with watchers con-
stantly on duty. The posts and in
struments were all connected to a
central station. When the watch
ers heard gun fired they touched
button that sent the current
through the delicate wire and start
ed the recording machinery in mo-
tion.. Then by means of relays and
other electrical apparatus we would
have the sound wave photographed
on a strip of moving picture film.
From this it was not difficult to de-
duce by mathematics the position de-
| sired
This little instrument not only
| told us, by means of the vibration
recorded, the location and kind of
gun firing but also the target being
! fired at. 1t was found that the diff
| ference of time between the sound
/ of the gun and the sound OF the
shell breaking the air gave a great
/ deal of this information. This lat
| ter sound must not be confused with