Hearing the Field 211
piece of glass barely covered in water ( figure 13.12a ). On July 2, he rang a glass by moving
a moistened finger around its lip ( à la Bacon and Mersenne) and drew its crispations ( figure
13.12b ) as “ little ridges apparently permanently standing out along the surface of the water
perpendicular to the glass, ” in contrast to “ places where the crispations were weakest, ”
marked × , which “ were breaking into confused heap like crispations. By diminish[ing] the
force of vibration the former almost entirely disappeared and the latter became simple
linear heaps perpendicular to the glass. Very good. ”^35
In his singing glass, Faraday approvingly noticed the interaction between vibrating
linear patterns, only “ apparently permanent, ” in its circular environment, thereby
linking the medium ’ s connection of circular and linear modes with the transience of
these effects. On July 18, he wrote his diary entry at the beach at Hastings (where he
was on vacation with his wife), noting the “ peculiar series of ridges produced by steady
strong wind on water on sandy shore. ” Going indoors, he “ vibrated round plate on lath
with water and sand so as to obtain circles and then square arrangement; the numbers
of intervals between the circles and between the heaps were the same for the same
plate, water, vibration, etc. etc. ”^36 Faraday dated the appendix to his paper on sound
figures July 30, 1831, showing that his work and thinking continued past his final diary
entry on this subject.
The very next entry in Faraday ’ s diary is dated August 29, 1831 (four weeks later):
“ Expts. on the production of Electricity from Magnetism, etc. etc. ” During the intervening
weeks, he had made an iron ring (about 2 cm in thickness and 91 cm in diameter) with
two sets of wire windings, labeled A and B in his sketch ( figure 13.12c ), separated and
insulated from each other so that no direct conduction of current could occur between
them. The B coil he connected to a galvanometer to measure the current; the A coil could
be connected to a battery. The moment of discovery was at hand, decisive yet subtle:
“ When the contact was made, there was a sudden and very slight effect at the galvanometer,
and there was also a similar slight effect when the contact was broken. ”^37 But when the
current through A was steady, there was no effect in B ; the effect was “ evident but tran-
sient, ” for “ it continued for an instant only, and partook more of the nature of the electrical
wave passed through from the shock of the common Leiden jar than of the current from
a voltaic battery. ”^38 Earlier researchers had overlooked this effect because of its transience:Figure 13.11
Faraday ’ s 1831 illustration of the typical sequence of patterns shown on a rectangular plate excited near its center
as the force of vibration increases (read left to right).