influence of Vibratory Motions. 17 
more developed ; that is to say, the limpid portion will appear 
still a little thicker, the continuous part will become still shorter, 
the ventral segments wider, and the nodes narrower. Moreover, 
the superposition of the ventral segments formed by each of the 
masses will be more exact, and thus they will overreach one an- 
other less toward their extremities, so that the ventral segments 
which result from their superposition will be more gathered 
together, and the nodes which separate the same will appear to 
be elongated. Now such is, in reality, as may be seenin No. 7 
of paragraph 3, the state of the jet under the influence in 
question. 
The phenomena would be still much more regular if the jet 
were in the first place protected from all foreign influences ; and, 
in fact, Savart speaks of the great regularity of the ventral seg- 
ments which manifest themselves when such a jet is received 
upon a stretched membrane which serves as a sonorous instru- 
ment for giving the unison. 
12. When the instrument employed gives a note not in 
unison with that of the jet, then as the vibrations no longer suc- 
ceed each other at the same intervals as the passages of the ex- 
pansions and contractions due to the forces of figure, there can 
no longer be an incessant concurrence between the two kinds of 
actions, and it will at once be perceived that very complicated 
effects must result from these alternations of accord and opposi- 
tion. Nevertheless we will attempt to unravel to some extent 
the phenomena then presented by the jet. 
To simplify our task as much as possible, we will assume all 
foreign actions to have been previously annulled. During the 
succession of phenomena, let us mentally seize the moment when 
the central point of a contraction due to the forces of figure passes 
the contracted section precisely at the same time that an ascend- 
ing vibration is half completed ; this vibration will then evidently 
concur with the forces of figure to increase the contraction. If 
the note of the instrument, however, has a higher pitch than 
that of the jet, in other words, if the duration of a vibration is 
less than that of the passage of the contraction, a greater or less 
portion of the bottom of the latter must have been in conflict 
with the end of the preceding descending vibration, and an equi- 
valent part of the top of the contraction will also be in conflict 
with the commencement of the succeeding descending vibration, 
because these descending vibrations tend to expand the portions 
of the jet upon which they act. If, on the contrary, the note 
produced by the instrument has a lower pitch than that of the 
jet, it is evident that a concurrence will exist throughout the 
whole of the contraction, but that the commencement of the 
vibration must have been in conflict with the upper part of the 
Phil. Mag. 8. 4. Vol. 14, No. 90. July 1857. C 
