On placing different metals in the meatus auditorius externus of both my ears, and establishing an insulated metallic communication between them, I felt, or fancied that I felt, a disagreeable jirk of my head. The metals used were a silver probe, a roll of tin-foil, and a common brass conductor belonging to an electrical machine. On withdrawing them from my ears, I experienced a feeling similar to that which one has after emerging from under water. I was not sensible of having hurt my ears by the experiment, nor had I any uneasy sensation after it; but, on getting out of bed next morning, I perceived both my pillow and my face stained with blood; and, on examining, found that it had come from one of my ears. An hæmorrhagy from this part had never happened to me before. From whatever cause this accident happened, (and it is highly probable that it arose from some hurt unperceived at the time), I need not say, that I have never repeated the experiment, and that I certainly never shall. I never could perceive, that the senses, either of touch or of smell, were in the least affected by the metals; but the effect which they produce upon the eye is very remarkable. Having laid a piece of tin-foil upon the point of my tongue, I placed the rounded end of a silver pencil-case, against the ball of my eye, in the inner canthus, and suffered them to remain in these situations till the parts were so far accustomed to them, that I could examine the sensations produced; I then brought the metals into contact with each other, and, to my surprise, perceived a pale flash of light diffuse itself over the whole of my eye. My tongue was at the same time affected with a similar sensation to that produced when both the metals are in contact with it. On darkening the room, the flash became more distinct, and of a stronger colour. This sensation is not the effect of pressure upon the eye, as in Sir Isaac Newton’s experiment; for no pressure should be used. All that is required, is, that the silver lie between the lids of the eye, and in contact with any part of the ball. If the experiment be made with zinc and gold, instead of tin-foil and silver, the flash is incomparably more vivid. I had the disagreeable opportunity of trying this experiment upon one of my eyes, in a state of inflammation; and, in this case, found the flash much more strong than it was in the uninflamed eye. I tried it likewise upon a patient, affected with amaurosis; but the man was so stupid that I could not satisfy myself as to the precise result.