88 
Proceedings of the Royal Society 
on exerting a much greater pressure by help of a small pencil of 
wood, no motion was perceptible, yet on bringing the knife-point 
within the field of view, but without pressure, the motion was re- 
newed, and the bubble was seen to approach the steel on whichever 
side it might be placed. The possible slight magnetism of the 
steel suggested itself as an explanation, accompanied, however, by 
the unheard-of occurrence of a magnetised fluid; and the blade 
was magnetised first in the one and then in the opposite way with- 
out any perceptible change of effect. Meanwhile Mr Davidson 
had found that a piece of soft steel occasioned the same motions. 
Pieces of brass and copper wire, printing type, silver and copper 
coin, all acted in the same way ; but pieces of wood, glass, ivory, 
showed no effect. . 
Afterwards, trials made with compact oxide of iron, and with 
sulphuret of lead, gave no perceptible result; yet, until the trials 
shall have been conducted with scrupulous care as to the horizon- 
tally of the upper surface of the cavity, we cannot hold the 
absence of action to be proved; but, as present appearances go, 
it seems that the metallic state is essential to this repulsion. 
By inclining the instrument, we may bring this repulsion to 
oppose gravity, and the degree of inclination affords a test of the 
amount, so much so that means for determining the law of its vari- 
ation by distance, and the specific influences of different metals, 
are brought within reach. 
Modifications in the arrangement of the microscope, so as to 
allow of the convenient exposition of specific masses, as well as to 
secure the measurements of the inclination and distance, are needed 
before we can obtain results reliable as to quantity ; when these 
modifications are completed I shall place the details before the 
Society. 
Boughly made, as at present, the experiments point to a specific 
intensity for each metal, and to a diminution in a ratio higher than 
that of the inverse squares of the distances. 
I have not been so fortunate as to find among the cavities in 
rock crystal, topaz, and amethyst, within my reach, any containing 
movable fluid : it is desirable that physicists, who may be in pos- 
session of such specimens, should examine whether this repulsion 
occur there also. 
