.330 
MR. FARADAY ON THE FORMS AND STATES 
made (72), giving 1 heaps that were two inches and a half wide each* ; and 
now it was evident, by ordinary inspection, that the heaps were not stationary, 
but rose and fell ; and also that there were two sets regularly and alternately 
arranged, the one set rising as the other descended. 
99. Sand gave no indications of arrangement with these large heaps (86) ; 
but when some coarse saw-dust was soaked, so as to sink in water, and then 
distributed in the fluid, its motions were beautifully illustrative of the whole 
philosophy of the phenomena. It was immediately washed away from under 
the rising and falling heaps, and collected in the places equidistant between 
these spots, as the sand did in the former experiments (86), and by its vibra- 
tory motion to and fro, it showed distinctly how the water oscillated from one 
heap towards another, as the heaps sunk and rose. 
100. When milk (75) was used instead of water for these large arrangements 
in a dark room, and a candle was placed beneath, the appearances also were 
very beautiful, resembling in character those described (97). 
101. Each heap (identified by its locality) recurs or is re-formed in two com- 
plete vibrations of the sustaining surface ■f-; but as there are two sets of heaps, 
a set occurs for each vibration. The maximum and minimum of height for 
the heaps appears to be alternately, almost immediately after the supporting 
plate has begun to descend in one complete vibration. 
102. Many of these results are beautifully confirmed by the appearances 
produced, when regular crispations have been sustained for a short time with 
mercury, on which a certain degree of film has been allowed to form { 77 )- On 
examining the film afterwards in one light, lines could be seen on it, coinciding 
with the intervals of the heaps in one direction; in another light, lines coin- 
ciding with the other direction came into sight, whilst the first disappeared ; 
and in a third light, both sets of lines could be seen cutting out the square 
places where the heaps had existed : in these spaces the film was minutely 
wrinkled and bagged, as if it had there been distended ; at the lines it was 
only a little wrinkled, giving the appearance of texture; and at the crossing 
* This estimate is given in accordance with the mode of estimating the former and smaller heaps, as 
if the heaps were formed simultaneously ; but it is evident that if only half the number exist at once, 
each heap will have twice the width or four times the area of those which can be formed if all exist 
together. 
f A vibration is here considered as the motion of the plate, from the time that it leaves its extreme 
position until it returns to it, and not the time of its return to the intermediate position. 
