and magnetic rotations. 497 
therefore analogous to that which produces the aberration of 
light. 
The essential circumstance in producing the rotation of the 
suspended magnet is, that the substance revolving below it 
shall acquire and lose its magnetism in a finite time, and 
not instantly. It appeared, therefore, that if any other 
attractive or repulsive property exists in matter which is 
capable of communication to other matter situated near it ; 
and if such communication require time for its performance ; 
and if, when it is communicated, the force is not instantly 
annihilated on removing the cause, then such a property of 
matter may be substituted in the preceding reasoning instead 
of magnetism, the same deductions may be made, and similar 
consequences may be expected to result. On reviewing the 
known properties of matter, electricity seemed to be the only 
one which satisfied the requisite conditions : imperfect con- 
ductors placed in the neighbourhood of excited bodies do not 
immediately attain a state of electric equilibrium ; and when 
they have arrived at that state which is due to such a posi- 
tion, on the removal of the excited body they do not instantly 
return to their former state. I therefore made the following 
experiments. 
Experiment 1. 
A needle was made of thin sheet brass, of the form, 
fig. 5, having two circular ends 1.25 inches in diameter, 
and the distance of their centres 3.1 inch; it had its edges 
coated with sealing-wax. Another similar needle was made, 
about one-third larger. One of these needles was suspended 
from a filament of silk, of several feet in length, at the 
distance of .25 inch above a circular glass plate six inches 
