The experiment which you mention, of filing your glass, is analogous to one which I made in 1751, or 1752. I had supposed in my preceding letters, that the pores of glass were smaller in the interior parts than near the surface, and that on this account they prevented the passage of the electrical fluid. To prove whether this was actually the case or not, I ground one of my phials in a part where it was extremely thin, grinding it considerably beyond the middle, and very near to the opposite superficies, as I found, upon breaking it after the experiment. It was charged nevertheless after being ground, equally well as before, which convinced me, that my hypothesis on this subject was erroneous. It is difficult to conceive where the immense superfluous quantity of electricity on the charged side of a glass is deposited.
I send you my paper concerning meteors, which was lately published here in the Philosophical Transactions, immediately after a paper by Mr. Hamilton on the same subject.
I am, Sir, &c.
B. FRANKLIN.
FOOTNOTE:
[91] This letter is translated from the French edition of Dr. Franklin's works, as are also all that follow, to the Appendix, the one to Miss Stephenson excepted. Editor.
[Mode of ascertaining, whether the Power, giving a Shock to those who touch either the Surinam Eel, or the Torpedo, be electrical.]
1. Touch the fish with a stick of dry sealing-wax, or a glass rod, and observe if the shock be communicated by means of those bodies.
Touch the same fish with an iron, or other metalline rod.