asuring
three inches in thickness and "deadened" with sawdust or shavings
between the layers of wood of which they are formed.

A few organs of Hutchings and other makers are provided with a double
set of shutters, so that sound waves escaping through the first set are
largely arrested by the second. The _crescendo_ and _diminuendo_ are
thus somewhat improved.

By the adoption of scientific principles Hope-Jones has multiplied the
efficiency of Swell boxes tenfold. He points out that wood, hitherto
used in their construction, is one of the best known conductors of
sound and should, therefore, not be employed. The effects produced by
his brick, stone and cement boxes (Worcester Cathedral, England; McEwan
Hall, Edinburgh, Scotland, Ocean Grove, New Jersey, etc.) mark the dawn
of a new era in Swell-box construction and effect. It is now possible
to produce by means of scientific Swell boxes an increase or diminution
of tone amounting to many hundred per cent.

We have heard the great Tuba at Ocean Grove, on 50-inch wind pressure,
so reduced in strength that it formed an effective accompaniment to the
tones of a single voice.

The Hope-Jones method seems to be to construct the box and its shutters
(in laminated form) of brick, cement or other inert and non-porous
material, and to substitute for the felt usually employed at the joints
his patented "sound trap." This latter is so interesting and of such
import in the history of organ building that we append, on the next
page, illustrations and descriptions of the device.

If a man should stand at one end of the closed passage (C) he will be
able to converse with a friend at the other end of the passage (D).
The passage will in fact act as a large speaking tube and a
conversation can be carried on between the two individuals, even in
whispers (Figure 12).

This passage is analogous to the opening or nick between Swell shutters
of the ordinary type.

If a man should stand in room 1 at A, he will be able to see a friend
standing in room 4 at B, but the two friends will not be able to
converse. When A speaks, the sound waves that he produces will spread
out and will fill room 1. A very small percentage of them will strike
the doorway or opening into room 2. In their turn these sound waves
will be diffused all through room 2, and again but a small percentage
of them will find access into room 3. The sound waves will by this
time be so much attenuated that the voi