450 Mr. D. J. Blaikley on the 
The one point which appears to me to be open to question 
is whether the rate of diminution of velocity is so great as his 
work appears to prove; for if this rate of diminution is ex- 
tended until we reach tubes of the size used in musical instru- 
ments, we should have a velocity much less than experiments 
show to exist in such tubes (compare with Kundt). Probably 
the want of perfect smoothness in Regnault's tubes may account 
for some of the difference ; but I think that it is doubtful 
whether the influence of the membranes closing his tubes was 
thoroughly allowed for, and feel that the question is still an 
open one. 
It has long appeared to me that useful results might be 
obtained by making use of tubes giving musical notes, as the 
pitch of a steadily sounding note can be readily determined 
within a remarkable degree of accuracy, and there should be 
no difficulty in determining the temperature within half a 
degree Fahr., which is equivalent to 6 inches in the velocity. 
(Experiment — Resonance of closed tube to fork of 512 vibra- 
tions, the length of the tube being modified during the expe- 
riment to show both the maximum and constrained or imperfect 
resonance.) (See paper in Phil. Mag. for May 1879.) 
Modifying this experiment by sounding the tube with an 
organ-pipe mouth, the disturbing influence of the contraction 
of area at the lip comes into play in addition to the correction 
for the open end ; so that, although the value of the latter is 
pretty accurately known, no measurement of velocity based 
merely upon the length of a pipe is at all reliable. By adding, 
however, a half-wave or wave-length to a stopped pipe, main- 
taining the original pitch, and measuring this added length, 
I hoped to be able to get reliable results. The observations, 
though agreeing very well indeed so long as the pressure 
remained constant, did not agree in their different series when 
taken under very slight differences of pressure, much less than 
would cause sensible variation through change of intensity, 
according to Hegnault's determinations. 
To properly understand the causes of these variations, it 
will be necessary to examine some of the results of imperfect 
or constrained resonance, and consider the separate and con- 
joined influences of (1) the blast, air-reed, or inducing current; 
(2) the prime tone of the resonating air-column; and (3) the 
higher or partial tones sounding with the prime; the pitch of 
the resultant note, or alternating induced current, depending 
upon the values of these three forces, which have a power of 
mutual influence within certain limits. The subject presents 
itself to my mind in the following way : — 
In the figure, let the blast from A cause the quarter-wave 
