Bismarck daily tribune. [volume] (Bismarck, Dakota [N.D.]) 1881-1916, 1905-03-24
A DISCUSSION; DIS IS; N
OF ACOUSTICS
WHAT TENDS 70 MAKE On MAI
ACOUSTIC PROPERTIES OF
81 5 u HALLS. i93
A LENGTHY PAPER ON AcoUs
TICS BY w. c. SABINE, AN
EXPERT. @


discussions in the legislature last.
winter regarding the acoustic pro
perties 81 the new house chamber,
Farmer Wallace calls the attention
Of the Tribune to the following article
on the subject Of acoustics and
whispering galleries, appearing from
the pen Of Wallace G. Sabine in the
Scientific American:
z ut has recently come to the
writer's attention that one of the
most curious and in its way famous
architectural features of Washington.
the whispering gallery in the old
house of representatives, now the
hall Of statues, has been unintentional-
ly destroyed. 1t became necessary to
replace the old ceiling, which was of
wood, by new ceiling. In order to
preserve the whispering gallery, a
feature which always interested, Wis
itors, the superintendent of the build
ing, who was in charge Of the recon
struction, had measurements made OF
the dimensions of the old ceiling and
reproduced them as accurately as
possible in the new. Notwithstand-
ing this care the whispering-ga gallery
property of the room almost entirely
disappeared, and since then the fact
has been frequently cited as another
OF the mysteries Of architectural
acoustics and a disproof of the posi-.
bility of predicting such phenomena.
So far, however, from being either a
mystery or a disproof of the accuracy
of the scientific considerations In
dealing with architectural acoustics,
this disappearance of the whispering
gallery is exactly the opposite, and
was in fact predicted by the writer
two years before in the American
Dictiontry of Architecture. Under
the head of Whispering Galleries
the dictionary being published in
1899, is the following paragraph:
Whispering galleries are usually
accidental, but may without difficulty
be predetermined. There are two
general types-focusing and conduct
ing. In the one the sound divergine
from the source is received upor
some concave rejecting surface, and
is concentrated again at the con
jugate focus. One of the best and
most accessible examples of this type
is the hall of statues, the old cham
Der of the house of representatives
in the capitol at Washington. The
ceiling of this Is very considerable
portion of the surface of sphere
| whose center is near the floor. Stand
| ing at the center of this sphere one
can hear his own whisper returned
to him. Standing at one side of this
point he can whisper, especially If he
turns his face toward the ceiling, to
person standing at a great distance
on the other side of the center. For
any position of the speaker there is
a corresponding point at which the
whisper is more or less accurately
focused. The ceiling, painted so that
it appears deeply paneled, is smooth.
Had the ceiling been paneled, the re-
Election would have been irregular.
and the effect very much reduced.
The most accurate form for whfs-
pering gallery is that in which the
rejecting surface is very consider
able portion Of the surface Of an
ellipsoid, that has for it's foci the two
points between which there Is to be
communication
The above, written before any
changes We're contemplated, exactly
covers the case. The new ceiling
differs from the old in two respects.
Instead of being Of wood it is OF plas-
ter on iron supports. This alone
would produce no deterioration In the
whispering gallery, for plaster on
iron is an even better reflector than
wood. But plaster as now handled
admits Of an architectural treatment
to which It did not formerly SO
readily lend itself, and the coffering
which was but painted on the old
ceiling Is copied in relief on the new,