Vibrations in the Air surrounding a Sounding Body. 391 
mirror I have distinctly detected a displacement of the flames 
on moving the resonator, (UT) over only 3 centimeters or 7th 
of a wave-length, and with the micrometer I feel assured that 
I can determine the wave-surface of a body giving the note 
UT, to one centimeter of its true position. Of course with 
higher notes we shall get a proportionally closer determination. 
But the object of this paper is not to present numerical results ; 
I reserve these for a subsequent communication, in which I will 
also present diagrams of apparatus and the appearances of the 
ames In various experiments. 
I will here remark that the success of the experiments de- 
pends on the resonator with its attached tube being in perfect 
unison with the organ pipe; also, the relative heights and posi- 
tions of the flames should be so adjusted that the sharpest 
definitions are obtained in the rotating mirror, and thus be able 
to detect and measure the effects of small changes in the position 
of the resonator ; but these and other manipulative details will 
readily occur to any physicist who repeats the experiments. 
Applications of the Method. 
lates of high theoretic interest which have heretofore been 
eemed beyond the reach of experiment. Its application to 
such are so numerous that they are almost co-extensive with 
the phenomena of sound. 
The actual experimental determination of wave-surfaces in 
free air and in buildings can now certainly be accomplished ; 
and such determinations may serve to extend our knowledge in 
the direction of giving the proper laws which should govern 
architects in their construction of rooms for public assemblies. 
the differences, if any, in the velocities of sound, corre- 
sponding to vibrations differing in intensities and frequencies, 
May be determined by the use of reflectors, and the direct 
Tom the capsules of pipe and resonator to contiguous jets, and 
adjust their flames to coincidence or to bisection of serrations; 
using for this purpose the manometric micrometer. Now sup- 
pose, for siipheuy: that the pipe gives 340 complete vibrations 
ma second; then, as the velocity of sound is 340 meters per 
Second, it is evident that in ath of a second an*aerial pulse 
will traverse one meter. Therefore, if all things else remain the 
