To Peter Collinson
Printed in Benjamin Franklin, Supplemental Experiments and Observations on Electricity, Part II. … (London, 1753), pp. 108–.1 (Yale University Library)
As you tell me our friend Cave is about to add some later experiments to my pamphlet,3 with the Errata,4 I send a coppy of a letter from Dr. Colden which may help to fill a few pages;5 also my kite experiment in the Pennsylvania Gazette: to which I have nothing new to add, except the following experiment towards discovering more of the qualities of the electric fluid.6 From the prime conductor, hang a bullet by a wire hook; under the bullet, at half an inch distance, place a bright piece of silver to receive the sparks; then let the wheel be turned, and in a few minutes (if the repeated sparks continually strike in the same spot) the silver will receive a blue stain, near the colour of a watch spring. A bright piece of iron will also be spotted, but not with that colour: it rather seems to be corroded. On gold, brass, or tin, I have not perceived that it makes any impression. But the spots on the silver or iron will be the same, whether the bullet be lead, brass, gold, or silver. On a silver bullet there will also appear a small spot, as well as in the plate below it.
One Mr. Watts promised in the Magazine, to write something on electricity;7 I have not yet seen it advertised.
1. Letter XI in the 1753 Supplement and in the next two editions of Exper. and Obser., but omitted in the 1769 and 1774 editions.
2. Undated in the printed version, this letter must have been written on or soon after October 19, since with it BF sent the description of the kite experiment printed in the Gazette of that date.
3. See above, p. 333.
4. The additional Errata were printed on the unnumbered last page of the Supplemental Experiments and Observations, Part II, 1753.
5. Whichever of Cadwallader Colden’s previous letters BF may have sent, none was printed in the 1753 Supplement or any later editions of Exper. and Obser.
6. The remainder of this paragraph appears twice in Supplemental Exper. and Obser., Part II (1753): as a part of this letter (pp. 108–), and also on p. 98 as an addendum, headed “An Experiment towards discovering more of the Qualities of the Electrical Fluid,” to the “Queries and Answers” BF enclosed in his letter to Colden, Oct. 31, 1751 (see above, pp. 202–5.)
7. Gent. Mag. for 1750 and 1751 prints several communications on electricity by W. Watts of Norton near Galby, Leicestershire, one of which refers to a longer treatise which “(if health permits) I propose speedily for the press.” Gent. Mag., XXI (1751), 9. The projected publication has not been found.