Chemistry and Physics. 483 
and we clearly perceive the first overtone, since, as we well know, 
the even overtones are strengthened and the uneven ones destroyed 
whenever the difference of half a phase of vibration oceurs in the 
two notes in unison. This octave [the first overtone] is also seen 
in the flame which produces a series of low broad images in the 
mirror each of which is cleft. It is well in this experiment to use 
greater ‘bregi of the air in order to increase the intensity of the 
octave in the 
Since this cpaest lia of the octave in the interference of two 
fundamental notes may be Sata vo beautifully | also by means 
communication with the tube leading to the pe te capsule ; 
which I did by means of gum tubes in such a manner that the 
upper wind box of the syren preserved a limited inabilit irks as to 
roduce and interrupt interference through its different _—— 
Yhenever we approach the point of interference of the upper 
large vibrations of the fu ideisbke! tone 
atti disappear, and the short cloven flame of the octave take 
ss 8 special apparatus, which I constructed for observing pheno- 
mena of inter st of different kinds, is based upon a method 
first used by Herschell, and after him ‘by other physicists. The 
principle gy in producing interference by allowing waves 
coming from the same source 
directions, differing in engi by half a wave-length, and then 
uniting them again. A t ube is used branc ching off in two direc- 
interference, we must introduce as simple e as possible into 
the tube by connecting it with a resonator before which the cor- 
responding Say React is sounded : now lengthen one of 
which is a manometric capsule, si shall hay? len thening one | 
ea how the deeply cloven flames in the revolving mirror are 
soaly’ dl a inte baachs of light when the difference of half 
wave-length is reached. Interference may be shown much more 
beautifully by means of another arrangement, Instead of allow- 
one. Ona stand are 
dle one bein, saved Seok oh o gum tubes. 
gas pipe of g) capsule with the highest burner, pa “poe “of the 
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