galton.org 253
Whistles for High Notes
253
instruments, having necessarily little depth, require to be made with very small bores.
The depth of the inner tube of the whistle at any moment is shown by the graduations
on the outside of the instrument. The lower portion of the instrument as formerly made for
me by the late Mr. Tisley, optician, Brompton Road,
[1]
is a cap that surrounds the body of
the whistle, and is itself fixed to the screw that forms the plug. One complete turn of the
cap increases or diminishes the depth of the whistle, by an amount equal to the interval
between two adjacent threads of the screw. For mechanical convenience, a screw is used
whose pitch is 25 to the inch; therefore one turn of the cap moves the plug one twenty-fifth
of an inch, or ten two hundred-and-fiftieths. The edge of the cap is divided into ten parts,
each of which corresponds to the tenth of a complete turn; and, therefore, to one two-
hundred-and-fiftieth of an inch. Hence in reading off the graduations the tens are shown on
the body of the whistle, and the units are shown on the edge of the cap.
The scale of the instrument having for its unit the two hundred-and-fiftieth part of an
inch, it follows that the number of vibrations in the note of the whistle is to be found by
dividing (13440x250)/4, or 84,000, by the graduations read off on its scale.
A short table is annexed, giving the number of vibrations calculated by this formula,
for different depths, bearing in mind that the earlier entries cannot be relied upon unless
the whistle has a very minute bore, and consequently a very feeble note.
Scale Readings
(one division = 1/250
of an inch
Corresponding
Number of
Vibrations per
Second
Scale Readings one
division = 1/250 of
an inch
Corresponding
Number of
Vibrations per
Second
10
84,000
75
11,200
15
56,000
80
10,500
20
42,000
85
9,882
25
33,600
90
9,333
30
28,000
95
8,842
35
24,000
100
8,400
40
21,000
105
8,000
45
18,666
11
7,591
50
16,800
115
7,305
55
15,273
120
7,000
60
14,000
125
6,720
65
12,923
130
6,461
70
12,000
[1]
Mr. Hawksley, surgical instrument maker, 307 Oxford Street, also makes these whistles, and
those he makes have much purity of tone.
