WHISPERING GALLERIES
261
discussion. It is sufficient to say that the general résultés a disper¬
sion or a distortion in the form of the focus and that the general
effect is to greatly reduce the efficiency of the whispering gallery,
but to by no means wholly destroy it, as would be the case with
complete irregularity.
By the term whispering gallery is usually understood a room,
either artificial or natural, so shaped that faint sounds can be heard
across extraordinary distances. For this the Hall of Statues was ill-
adapted, partly because of a number of minor circumstances, but
primarily because a spherical surface is accurately adapted only to
return the sound directly upon itself. When the two points between
which the whisper is to be conveyed are separated, the correct form
of reflecting surface is an ellipsoid having the two points as foci.
When the two points are near together, the ellipsoid resembles more
and more a sphere, and the latter may be regarded as the limiting
case when the two points coincide. On the other hand, when the
two foci are very far apart the available part of the ellipsoid near one
of the foci resembles more and more a paraboloid, and this may be
regarded as the other extreme limiting case when one of the foci is at
an infinite or very great distance. I know of no building a consider¬
able portion of whose wall or ceiling surface is part of an exact ellip¬
soid of revolution, but the great Mormon Tabernacle in Salt Lake
City is a near approximation. Plans of this remarkable building do
not exist, for it was laid out on the ground without the aid of formal
drawings soon after the settlers had completed their weary pilgrim¬
age across the Utah desert and settled in their isolated valley. It was
built without nails, which were not to be had, and held together
merely by wooden pins and tied with strips of buffalo hide. Not¬
withstanding this construction, and notwithstanding the fact that it
spans 250 feet in length, and 150 feet in breadth, and is without any
interior columns of any sort, it has been free from the necessity of
essential repair for over fifty years. As the photograph (Fig. 5)
shows, taken at the time of building, the space between the ceiling
and the roof is a wooden bridge truss construction. These photo¬
graphs, given by the elders of the church, are themselves inter¬
esting considering the circumstances under which they were taken,
the early date and the remote location.