— 41] 
LI. Experimental and Theoretical Researches on the Figures of 
Equilibrium of a Liquid Mass withdrawn from the Action of 
Gravity —Third Series. By J. Pratreav. 
[Concluded from p. 22.] 
§ 15. oe order to terminate that which relates to a note pro- 
duced at a distance and different from unison, we have 
still to account for the facts stated in No. 10 of paragraph 3. 
We proceed to show from a theoretical point of view, that 
these facts, with the exception of the last, depend upon a more - 
general principle, which may be thus enunciated: if the vibra- 
tions of the instrument are sufficiently energetic with respect to 
those occasioned by the shock of the detached masses, and if at 
the same time the interval between the two notes is not too 
great, the note of the jet may be brought into unison with that 
of the instrument. We may remark that these are the circum- 
stances cited in No. 10 of paragraph 3; for when the jet: falls 
upon a body which can only render a determinate note, such as 
a diapason, and if we suppose for a moment, that the former 
suffers no modification with respect to the number of detached 
masses, then the vibrations due to the shock of these masses will 
in general have a period different from that of the vibrations of the 
body impinged upon, and hence the former can only be thus pro- 
duced: every time a mass reaches the body, air is expelled from 
between the two, and then returns in order to be expelled anew 
on the arrival of the followmg mass, and so on. Now the sono- 
rous waves thus produced are necessarily very feeble when com- 
pared with those resulting from the vibrations of the body which 
receives the shocks; besides this, the interval between the two 
tones can be diminished at pleasure by causing either the charge 
or the diameter of the orifice to vary. 
As the vibrations of the instrument—or, in the case under con- 
sideration, those of the body receiving the shock—which are 
transmitted by the air to the vessel and to the liquid have not 
the same period as the passages of the contractions and expan- 
sions due to the forces of figure, there is, as we have explained 
($12), avarying conflict between the two kinds of action; but if the 
interval between the two notes is not too great, it is conceivable 
that the transformation of the jet-—a phenomenon susceptible of 
being influenced by extraneous causes*—may, under the action 
of vibrations, so lengthen or shorten the nascent contractions 
and expansions that the time of passage of each of the latter 
shall be precisely equal to the period of a vibration, and the 
two kinds of actions constantly in agreement: this point being 
attained, the note of the jet must necessarily be in unison with 
* Second Series, § 58. 
