Benjamin Franklin to Peter Collinson, October 1, 1752

[October, 1752] 2

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.