And the refult of thefe actions, upon the whole, may be suppofed fuch a compreffon or increafe of denfity in the aether, as muft agitate its Particles, with vibrations analogous to thofe which are excited in the air by the difcharge of guns, by thunder claps, or by any other method of caufing a fudden and violent compreffion in it.
Secondly, We are to conceive, that the vibrations thus excited in the aether will agitate the fmall particles of the medullary substances of the fenfory nerves with fynchronous vibrations, in the fame manner as the vibrations of the air in sounds agitate many regular bodies with corresponding vibrations or tremblings.
David Hartley, Observations On Man, His Frame, His Duty, His Expectations, 1749
Hartley developed a doctrine of vibration and association as a means of examining among other things memory and perception.
I would like to reassure readers that this is a fish aided observation that will become clear when fish trembling (an older idea in the history of fish electricity) comes up for discussion.