WITHDRAWN FROM THE ACTION OF GRAVITY. 323 
differ too much from one another, we can conceive that the transformation of 
the vein, a phenomenon susceptible of being influenced by extraneous causes, 
(2d series, § 58,) may, under the action of the vibrations, lengthen or shorten 
the incipient constrictions and dilatations, in such manner that the duration of 
the passage of each of them shall be precisely equal to that of a vibration, and 
that the two kinds of action shall be constantly in accord; this point being at- 
tained, the sound of the vein will be necessarily in unison with that of the in- 
strument. Only, for the vibrations of the instrument to be capable of realiz- 
ing that result, it is obviously necessary that they should have a suflicient de- 
gree of energy relatively to the vibrations of the sound proper to the vein, 
since these last tend to favor the normal action of the configurative forces. 
We shall better comprehend the phenomenon by considering it under a point 
of view a little different. Let us remember that the vibrations tend of them- 
selves to produce, in the vein, incipient constrictions and dilatations, (§ 5;) now, 
if these, constrictions and dilatations are a little superior or a little inferior in 
length to those which the configurative forces on their side tend to, originate, 
and if moreover the action of the vibrations is energetic enough to control 
that of these forces, the system of incipient constrictions and dilatations which 
will be formed must be that which depends on the vibrations, and hence the 
transformation thus modified at its origin will be completed after this new 
manner. 
But this state of the vein is a forced one, since the natural mode of transfor- 
mation is altered. Hence, if something suddenly disturbs the succession or 
regular transmission of the vibrations, the configurative forces ‘will at once be- 
come again preponderant, and the incipient contractions and dilatations will 
resume the length which corresponds with the free action of those forces. Thus 
is explained without difficulty the statement of No. 10, § 3, that it often re- 
quires but a slight blow given to the apparatus or a change in the position of 
the body struck suddenly to restore the sound of the vein to the tone which is 
proper to it. We have.supposed that, in the experiment referred to, the sound 
of the vein is restored to unison with that of the body receiving the impact, 
conformably with the principle advanced at the beginning of this paragraph. 
Savart, however, as may be inferred from the statement in the number in ques- 
tion, does nét express himself in this respect in precise terms: he merely says 
that the sound of the body struck modifies that of the vein, that it changes its 
period; but other experiments which we shall presently discuss:authorize us to 
ascribe to these words the sense we have given them. 
§ 16. We further learn from No. 10 of § 3, that when the difference of the 
two sounds is very small, these two sounds may make themselves heard periodi- 
cally or even simultaneously. Let us try likewise to explain these facts. 
We will suppose, for the sake of distinctness, that the sound proper to the 
vein is somewhat graver than that of the body struck. In the case of exact. 
unison, the number of impulses of the masses in a given time would be half 
the number of the vibrations of the body in the same time, and consequently the 
interval between two successive impulses would be equal to the duration of two 
of these vibrations; therefore, upon the above supposition, the interval between 
two impulses will a little exceed the duration of two vibrations, and if the re- 
action of these vibrations on the incipient constrictions and dilatations is not 
sufficiently powerful to modify the length and thus produce unison, the small 
excess of duration of the intervals in question will be maintained. This pre- 
mised, let us begin with the first impulse. This will cause the body to perform 
a vibration directed from above downwards, which will be followed by a vibra- 
tion from below upwards; then, a little after the commencement of a new de- 
scending vibration, the second impulse will arrive; the third will act during 
the third descending vibration, but at a little more advanced phase of that vi- 
bration; the fourth impulse will take place during the fourth descending vibra~ 
