320 
MR. FARADAY ON THE FORMS AND STATES 
rectangularly with extreme regularity ; permanent^ (in appearance), so long as 
a certain degree of vibration is sustained ; increasing and diminishing in height, 
with increased or diminished vibration ; but not affected in their lateral extent 
by such variations, though the whole crispated surface is enlarged or diminished 
at those times. If the plate be vibrated, so as to produce a different note, the 
crispations still appear at the centre of vibration, but are smaller for a high 
note, larger for a low one. The same note produced on different sized plates, 
by different modes of vibration, appears to produce crispations of the same 
dimension, other circumstances being the same. 
66. These appearances are beautifully seen when ink diluted with its bulk 
of water is used on the plate. 
67- It was necessary, for examination, both to prolong and enlarge the effect, 
and the following were found advantageous modes of producing it. Plates of 
crown-glass, from eighteen to twenty-two inches long, and three or four inches 
wide, were supported each by two triangular pieces of wood acting as bridges 
(18), and made to vibrate by a small glass rod or tube resting perpendicularly 
at the middle, over which the moist fingers were passed. By sprinkling dry 
sand on the plates, and shifting the bridges, the nodal lines were found (usually 
about one fifth of the whole length from each end), and their places marked 
by a file or diamond. Then clearing away the sand, putting water or ink upon 
the plate, and applying the rod or fingers, it was easy to produce the crispa- 
tions and sustain them undisturbed, and with equal intensity for any length 
of time. 
68. By making a broad mark, or raising a little ledge 
of bee’s wax, or a mixture of bee’s wax and turpentine, 
it was easy to confine the pool of water to the middle 
part of the plate, fig. 13, where, of course, the crispations were most powerfully 
produced. Such a barrier is often useful to separate the wet and dry parts of 
the glass, especially when a violin bow is used as the exciter. 
69. In other experiments, deal laths, two, three, or four feet long, one inch 
and a half wide, and three eighths or more of an inch in thickness, were used 
instead of the glass plates. These could be made to vibrate by the fingers and 
wet rod (67), and by either shifting the bridges or changing the lath an almost 
* Webeu’s Wellenlehre, p. 414. 
Fig. 13 
