210 Chapter 13
Faraday dated his draft paper on acoustical figures March 21, 1831, and sent it to
Wheatstone, who responded in a detailed letter two days later, showing that they remained
in contact during this new phase in which Faraday was conducting and writing his own
version of these phenomena. Wheatstone ’ s reply emphasizes the correctness of Faraday ’ s
experiments and inferences, contra Savart. In passing, Wheatstone mentions that he had
shown his own experiments to Young, thus closing the circle with the older generation of
wave theorists. Wheatstone also reminds Faraday of one of the techniques they had used
in an 1830 joint lecture, which Wheatstone uses to give another disproof of Savart. Wheat-
stone ends by noting the “ twofold importance ” of Faraday ’ s experiments both for “ the
investigation of the residual phenomena of elastic surfaces ” and “ further valuable informa-
tion from the application of similar considerations to other phenomena with which they
are intimately connected. ”^32 Given their shared history, these “ other phenomena ” may well
have included the velocity of electricity.
Though many of the effects collected in his 1831 paper concern steady-state phenomena,
Faraday often notes the transient quality of their onset or disappearance. For instance, he
notices how “ a strong steady wind ” excites “ stationary undulations ” forming uniform
ridges on the surface of shallow water. Such ridges can also have a transitory quality and
are also seen “ on the pavements, roads, and roofs when sudden gusts of wind occur
with rain. ” Faraday deduces that these are not ordinary deep-water waves but physically
different in causation and form, “ due to the water acquiring an oscillatory condition ... ,
probably influenced in some way by the elastic nature of the air itself and analogous to
the vibration of the strings of the Aeolian harp, or even to the vibration of the columns of
air in the organ-pipe and other instruments with embouchures. ” Faraday also thinks gases
and vapors can show analogous effects, “ their elasticity supplying that condition necessary
for vibration which in liquids is found in an abrupt termination of the mass by an uncon-
fined surface. ”^33 This spatial abruptness echoes the temporal suddenness he remarked in
the gusts of wind causing ridges on a wet surface.
The collocation of temporal and spatial effects is evident in Faraday ’ s descriptions of
the striking changes in the geometry of the patterns, whose beauty he remarks at many
points. Using a rectangular plate, he notices a characteristic time sequence beginning with
circularly symmetric patterns centered on the source of excitation; increasing the force of
vibration leads eventually to a surprising shift to a quadrangular pattern, first diagonal,
and finally square ( figure 13.11 ). Faraday notes that the reflected image of these patterns
is not stationary, but rather “ moves so as to re-enter upon its course, forming an endless
figure, like those produced by Dr. Young ’ s piano-forte wires or Wheatstone ’ s kaleido-
phone, varying with the position of light and the observer, but constant for any particular
position and velocity of vibration. ”^34 Evidently, Wheatstone ’ s little instrument (and its fili-
ation with Young) had remained in Faraday ’ s mind.
Faraday ’ s diary records his attention to the interplay between circular and rectangular
symmetries in his experiments. On June 17, he drew the circular crispations on a round