OF FLUIDS ON VIBRATING ELASTIC SURFACES. 
325 
it up altogether : if the vibratory force be gradually diminished, then the heaps 
as gradually fall, but without returning through the order in which they were 
produced. The following lines may serve to indicate the course of the phe- 
nomena. 
Fig. 14. 
When perfectly formed, the heaps are also to the number of ten in three inches 
with the same depth of water as that which produced the rings. The inter- 
vals between the rings and the heaps are the same, other influential circum- 
stances remaining unaltered. 
84. Then another form of heaps occasionally occurred, but always passing 
ultimately into those described. These heaps were grouped in an arrangement 
still very nearly rectangular, and at angles of 45° to the sides of the plate, but 
were contracted in one direction, and elongated in the other ; these directions 
being parallel to the sides and ends of the plate. If the marks 
in fig. 15 be supposed to represent the tops of the heaps, an 
idea of the whole will be obtained. Three inches along these r_Z“_r_TJZ 
heaps included eight, but across them it included fifteen nearly. “-T"-! - -! - -! 
These numbers are therefore the relation of length to breadth. 
But along the lines of the quadrilateral arrangement three 
inches included eleven heaps, which, notwithstanding the difference in form, 
is the same number that was produced by the same plate, with the same 
depths of water, when the heaps were round ; therefore an equal number of 
heaps existed in the same area in both cases ; and the departure from perfect 
rectangular arrangement, and also the ratio of 1 : 2, is probably due to some 
slight influence of the sides of the plate. 
85. When mercury covered with a film of very dilute nitric acid is vibrated 
( 77 ), the rectangular arrangement is constantly obtained. When vibrated 
under dilute ink (78), it is still more beautifully seen and distinguished. The 
tin plate sustaining the mercury was square, and when the whole surface was 
covered with crispations, the lines of the rectangular arrangement were always 
at angles of 45° to its edges. 
