Evening star., 1901-12-14
TRANSMISSION or SOUND
RESULTS OF EXPERIMENTS By
EMINENT PHYSICISTS.
Atmosphere which Resists the Boom
of Cannon-Scfentf1c Inquiry
Into the Subject.
From the London News.

/
At the time of the late queens funeral
popular attention was called to some Of
the vagaries of sound. The well-marked
reports of the minute guns which were
fired by the ships of Spithead as the sad
procession wound its way down their line
were heard at places whose geographical
position made very curious figure on the
map. At Richmond. for instance, more
than sixty miles in a straight line from the
scene, the sound was heard most distinctly.
and the concussion even caused windows 10
rattle. Even as far away as Cambridge
| and Peterborough the unmistakable reports
were family heard. Yet a number of OBJ
servers much nearer to Spithead all agreed
| that at many places within radius of ten
| to forty miles from the ships the sound
| OF the firing was quite inaudible. 1t is not
| easy to see why this should have happened.
| We are accustomed to think of the atmos-
phere as equally transparent to sound in
| all directions; indeed. we have given prac-
| tical effect to that belief for many CEN
turies by marking dangerous rocks with
bells or other sound signals to warn ships
| away from them in fog. Too often our be-
| lief in their efficacy has led to melancholy
disasters. of whose record there is no lack
| in the wreck lists at Lloyd's. II is only
| quite lately that physicists have seriously
grappled with the problem of the transmits
| sion of sound. In this country the classical
researches on that head are those of the
! late Prof. Tyndall, and at the present mo-
ment they are being carried on with COM
| mendable vigor by the Rev. j. NJ. Bacon,
who describes some Of his latest work In
| the October number of the Nineteenth Gen.
| tury and After. Mr.. Bacon gives a very
striking instance of that popularity in the
1 transmission of sound which was noticed
| at the time of the queens funeral During
the American civil war battle was fought
| in the valley of the Chickahominy, at a
| place where the river runs between two
| low ranges of hills about mile and half
| n yIh m a
pened to be a trained man of science,
watched this fight, on a beautiful after
noon, from the range Of hills opposite to
the firing line.
A Silent Battle.
| To his amazement, it was silent fight.
| as IL 1t had all been a dream. Looking
for nearly two hours" he writes, from 5
| to pm, on midsummer afternoon, at a
battle in which at least $4,000 men were
actually engaged, and doubtless at least a
1 hundred pieces Of field artillery, through
| an atmosphere optically as limpid as pos
sible, not a single sound of the battle was
audible to General Randolph and myself"
| The explanation of this amazing fact is
! simply that the air is sometimes as opaque
| to sound the thickest London fog is to
light, though the two states have no neces-
sary connection with one another. 1t Is un-
necessary to point out what danger to ship
| ping Is involved If optical and an acous-
tic fog happen to coincide, and how many
be thus explained, or the consequent i'm
portance of studying the transmission Of
sound more thoroughly than has yet been
attempted.
ginning in this strangely neglected work.
He gave a rational explanation of such
phenomena as We have mentioned. as well
| as of the frequent failure of the most pow
erful siren to make its warning audible at
| the right place. He showed by a long
course of ingenious and beautiful expert
ments that sound is reflected from or re-
| fracted by layers of air of different dem
stiles and temperatures anu degrees Of
| moisture, exactly as light is modified or ex-
tinguished in passing from one medium to
| another. In one case of reflection the
sound may be wholly stopped, in the same
way as heap of powdered glass or snow is
Opaque to light, though all its particles are
| individually translucent, because each tiny
| fragment reflects some of the light and
| finally none is left to get through. Refrac-
| ton may be as dangerous, because 1t bends
the sound out of its normal straight line
and makes 1T seem to come from a direc-
ton quite different to the true one so that
| a captain who thinks he is steering well
1 away from a warning siren or bell buoy
may be really running into danger. Any
one who has tried salmon spearing or has
even noticed the way in which a stick
thrust into water appears to be bent. will
readily understand this. A good example
of the way in which sound may be stopped
| by certain atmospheric conditions is afford
ed by the battle already mentioned. There
eral belts of air varying in the amount of
| watery vapor, and probably temperature,
arranged like laminae at right angles to
| the acoustic waves as they came from the
battlefield" The valley was partly swamp
| and partly cultivated fields; some Of 1t was
| In shelter, some in sunshine.
Zones of AudibiIity.
Every one knows that the belts Of air
above each of these regions would vary in
| moisture and temperature, and listening
| through these was like trying to see through
| water full of boiling eddies and cross cur
rents. Thus 1t is well known that ships can
come within less than O mile of the gi-
gantic siren at st. Catherines-s well de-
scribed in one OF Mr.. Kiplfng's cleverest
| stories-without hearing a sound from it.
| though it was believing with all its thous-
and-braZen-bul power. A foghorn some
| times behaves I'm the most capricious man
| ner; 1t is inaudfble near at hand, and be-
comes audible as one goes little further
of. There may be a regular series Of zones
of audibility and inaudibility, which makes
| 1t very pleasant for the navigator who Is
| feeling his way into harbor in a fog, by
| the help OF the lead and the voice Of the
| siren. In the case Of the funeral minute
guns. 1t is probable that the sound was
| thus stopped in some directions and In
others carried up into the air. and then
again reflected downward, so that 1t was
| not heard twenty miles away, but was
quite distinct twenty miles further or
1t may seem odd that we should still
| know comparatively little about the trans
| mission of sound. Yet the case is so, and
Mr.. Bacon describes many somewhat ele-
| mentary experiments by which he is ad-
vancing our knowledge. He is the first, SO
| far as we know, who has had the happy
thought of using a balloon for the purpose
Of investigating the behavior of sound In
| the upper regions of the atmosphere Many
Londoners have heard his speaking trum-
pet or his four-ounce charges Of guncotton
whose operation he now recounts in an in
teresting manner. 1t is, curious that we >.
should be able to calculate the motions of
light so much better than those of sound
We have plenty of statistics as to the be-
havfor OF our light house illuminants in fog
or haze, and every astronomer can make
the necessary corrections for the refraction
OF light by our atmosphere
Parliament TO Meet.
From the London Chronicle
The announcement that parliament WIN
meet on January 16 need cause no surprise
on account Of the early date though of "a