From Joseph Priestley
ALS (incomplete): American Philosophical Society
[First part missing] ly; and in a direct line, I some times inclosed them [in?] small glass tubes.
I make these experiments with great care, as my machine is constructed so as to electrify with equal strength by the rubber, or by the conductor, and I can change the mode of operation in an [instant?].3
I am still in a course of experiments upon glass [torn] but have not yet brought any thing to a state worthy of presenting to you. Many things have occurred which surprize and puzzle me, but that gives me no concern.
I have desired Mr. Canton and Mr. Price to show you the letters I have written to them. I gave Mr. Canton an account of experiment which proves that glass, when red hot, is pervious to electricity.4 Dear Sir, the sense I have of the honour of your acquaintance, and the pleasure I have in communicating to you the result of my little experiments, give me an ardour in these pursuits, which I never felt before. I am with the greatest respect, and with compliments to Messr. Canton and Price, your &c.
Addressed: To / Dr Franklin / at Mrs Stephens’ / in Craven street, in the Strand / London
2. This fragment is devoted to Priestley’s electrical experiments and, since he was busy performing them in 1766 for his own edification and for the purpose of writing his History of Electricity with greater confidence, it is dated in this year. It is quite possible that the letter was written in the winter or the early spring of 1766 because Priestley mentions having sent John Canton an account of an experiment “which, proves that glass, when red hot, is pervious to electricity” and in letters to Canton of Feb. 14, 1766, and March 29, 1766, he describes two experiments he has made to prove this point. Robert E. Schofield, A Scientific Autobiography of Joseph Priestley (1733–1804) (Cambridge, 1966), pp. 15, 26–7.
3. Priestley described this machine in History of Electricity, pp. 530–4, and illustrated it in Plate vii.
4. Priestley described in History of Electricity, pp. 610–11, the experiment on this matter that he had reported to Canton on Feb. 14, 1766.