influence of Vibratory Motions. 448 
if then we pass from the first to the second limit, by causing the 
direction according to which the jet issues to vary by degrees, 
the sheaf will not begin to manifest itself distinctly until a cer- 
tain angle between this direction and the descending vertical line 
is attained, and it will cease to be very apparent beyond another 
determinate angle. Further, as long as the jet issues in ob- 
liquely descending directions, and even in a horizontal direction, 
it is evident that at the extremity of the continuous portion— 
which portion is generally tolerably long—its direction will be 
already too near the vertical for the sheaf to manifest itself di- 
stinctly, so that the first direction at which the sheaf will com- 
mence to be visible will be an obliquely ascending one. All these 
conclusions agree with the facts of the No. under discussion. 
As will be seen, we admit that the imequalities between the 
nascent contractions do not depend upon the direction according 
to which the jet issues; and, in fact, there is no plausible reason 
for attributing these inequalities to the ascending obliquity of 
the jet. In treating of vertically descending jets, these inequal- 
ities were not mentioned, because in such cases they cannot 
occasion any phenomena of a peculiar kind; their only effect, 
then, is to augment a little in the axis of the jet the imexacti- 
tude of the superposition of the individual systems of ventral 
segments and nodes, and thus they merely constitute an influ- 
ence to be added to those mentioned in paragraph 10. The 
nature of the disturbances which produce the imequalities in 
question, it would no doubt be rather difficult to discover ; but 
whatever it may be, the dispersion of the discontinuous part in 
jets issuing at a suitable angle reveals to us the presence of these 
causes. 
§ 26. A jet being allowed to issue under an angie such as to 
cause the sheaf to be well formed, let us now conceive it to be 
submitted to the influence of a sonorous instrument. The note 
which will most shorten the continuous part will again evidently 
be that whose vibrations succeed each other at the same intervals 
as the passages at the contracted section of the expansions and 
contractions due to the forces of figure ($§ 5 and 12). But 
these vibrations being perfectly regular and isochronous, will, if 
sufficiently intense, prevent the disturbing causes from modifying 
the nascent contractions ; in other words, when activating the 
transformation they will impart to the same their own regularity, 
so that the nascent contractions will have the same length, and 
thus all the detached masses will describe precisely the same tra- 
jectory (§ 25): under the influence of the note, therefore, the 
sheaf ought to disappear, and the whole ought to reduce itself 
to a single jet presenting a perfectly regular system of ventral 
segments and nodes. 
