The Washington times., 1921-02-20

directionai wireless and "echo direction"
II was difflc1lt matter to locate the posi-
tion Of distant big gun, because an ex-
plosion produces sudden impulse propa.
gated equally fl all directions. In locating
guns the physicists used three wireless
telephone receivers, in known positions.
and were able to locate approximately the
direction Of the explosion. A modification
OF the sams apparatus was used IN locating
shibs d SEA.
Seientihc investigators have experiment
cd with sound-waves Of 5000 to 10000 peri
eds per ssoond, which IL far below the short
est wavs.psriods audible by man when such
b beam VI soand Of high frequency. COM
pafsbts 10 q seAfehilsht. falls Upon an OBJ
stasie, Il ID rehected or echoed, and the
echo ID detected BY hydfophone. An in
strumeht based on this idea has proved
somewhat useful In detecting rocks and
ships, but not In iocatins icebergs, which
have elastic properties similar to those of
water.
The ears Of man are very uncertain and
unreliable IA detecting the direction of
sounds, even when these are loud enough
10 be heard. BY increasing the distance
bstwsen mans two ears by means of an
apparatus q grsat ihcrsase Of accuracy in
locatius the direction OF sound is obtained.
Another apparatus has been invsnted to
give the blind man knowledge Of his sur
roundings through his ears ~ the bat re-
csives its Impressions.
On the other hand, the bat is able to
locate the position of objects very ac-
curAteiy, even though It's funny ears are
very close together. because the sounds
emitted and reflected to its ears are of
very short wavealength.
Bats possess powers OF flight superior
tn that OF many birds. This may be in
ferred from the fact that red bat has
been known to catch flies in the air while
birdehed with yeung that together
weighed more than she did.
Most California bats catch and devour
prey on the wing They bite off and re-
ieet the hard parts OF insects. In the
Autumn bats become very fat, ready for
migration or hibernation. Even the bats
on the wing all the year rely on this
stored fat to balance scarcity Of insects
Pats are as valuable to men as are any
OF the insectivorous birds. They are re-
iehtless and untiring hunters and destroy
ers OF mosquitoes. and this makes 1t very
desirable To encourage them San Antonio
Texas, and other towns have constructed
''bat roosts" In order to encourage the lit
tie animals to breed and destroy mos
quitoes. The bats attack nearly all the
nocturnal insects, especially the disease
carriers.
They are very difficult 10 shoot because
of their swift. errstic flight. Il has been
asserted by some raturalists that they
have the power to dodge shot through
their phenomenal sense.
They are powerful swimmers and have
the habit Of going into the water in
search Of insects.
In connection with the power Of bats to
avoid obstacles IN the dark II is interest.
Ing to recall the explanations that have
been advocated Of the blind mans power
OF avoiding collisions Persons who have
been long blind often show a remarkable
ability to avoid collisions with wallis, posts
and other lifeless objects. Professor G. f.
Fraser. OF Nova Scotia, has shown that
this is because person In moving drives
slight wave OF air before him When this
strikes a solid object Il Is thrown back
and some Mind men are clever enough to
perceive the proximity OF solid objects in
this. II mas been argued not unreasonably
that the bats power to avoid obstacles was
due to similar conditions, but investiga
tion seems to prove that the animals
power is too delicate and unerrtng to be
explained In this way.