20 M. J. Plateau on Jets of Liquid under the 
present, in a manner analogous to, though less decided than the 
case of unison, a small increase in the thickness of the limpid 
portion, and a system of ventral segments and nodes in the 
agitated portion; 4th, the development of all these phenomena 
ought to be less perfect the more the note of the instrument 
deviates from unison, so that notes having too high or too lowa 
pitch ought to appear inactive. 
We have assumed that all foreign actions were previously 
neutralized; but since these actions tend to produce similar 
effects (§ 10), it is evident that if they are left unneutralized 
they can scarcely do more than add to the intensity of the phe- 
nomena. 
We may here intimate, that notes not in unison with that of 
the jet at the same time give rise to other effects, which, in general, 
though not very apparent in jets descending vertically, manifest 
themselves, as will be seen, when the efflux takes place under 
certain obliquities. These effects depend upon the conflict be- 
tween the vibrations and the forces of figure, and consequently 
vanish in the case of unison; instead of diminishing, therefore, 
like the effects just studied, the ones now alluded to increase 
with the divergence from unison. 
§ 18. The first of the four conclusions above enunciated is 
precisely verified, in a particular case, by the fact recorded in 
No. 9 of paragraph 3. In fact, when the note of the instrument 
is very near that of unison, the period of vibration differs very 
little from that of the passage of a contraction or an expansion ; 
and consequently, when a coincidence takes place, it will be 
nearly complete, that is to say, the conflict will extend only over 
extremely small portions of the contraction or of the two adja- 
cent expansions; for such a contraction, therefore, almost the 
same things will take place as in the case of perfect unison ; 
hence at the moment when this contraction is ruptured, the 
continuous part of the jet will have nearly the same length as in 
the case of unison ; afterwards its length will increase until that 
corresponding to the greatest conflict is attained; but, in conse- 
quence of the near approach to equality between the respective 
periods of a vibration and of the passage of a contraction or ex- 
pansion, a considerable time will elapse before this maximum 
occurs, so that the gradual elongation of the continuous part will 
take place slowly enough to become perceptible ; lastly, the same 
things will occur with the subsequent shortening of the conti- 
nuous part, and so forth. As to the beats, it is clear that they 
result from the mutual reaction of the note of the instrument 
and that of the jet; for although Savart does not expressly say 
so, we may conclude from the manner in which he adduces the fact 
in question, that the jet ought to fall upon a stretched membrane. 
