From William Vaughan
ALS: American Philosophical Society
London Aug. 1st. 1782
I am happy that the inclosed gives me an opportunity of writing a line to one I have ever been taught to revere & respect. There are few Events I have so much at heart as once more enjoying your company. I hope from a change of men system & times that day may not be far distant. We have been too long accustomed to misfortunes not to rejoice at the least glymse of hope.
I saw yesterday a lense whose powers you are not perhaps unacquainted with. Platina melts in Seventeen Seconds & other metals yeild to its power. The weather has not been favorable for a variety of experiments. Parker has however many in contemplation with the assistance of our philosophical men here. I beleive it is found superior to the one in France. The lense is solid, & weighs 212 pd.3
Our friends Dr. Price & Dr. Preistley are well & would with our family join in sincere wishes for your health & happiness if they knew of this opportunity. I thank you for your generous concern about John who is released on his parole by Sir G. Carleton. He was well at Philadelphia May 10—4 With great respect & esteem I remain Dear Sir Your sincere & obt Servt
3. What William Parker called his “Large Lens” was in fact an instrument that focused the sun’s rays through two lenses mounted in a “Trunkated Cone” of wooden ribs. The larger lens, weighing 212 lb., measured three feet in diameter in the frame. The smaller lens weighed 21 lb. and measured 16 inches in the frame. (For comparison, the lens used by Priestley in his famous 1774 experiments was only 12 inches in diameter.) A wooden bar attached to the cone and extending beneath it held a small adjustable platform on which would be placed the substance to be melted, or “fused.” This entire structure was mounted in an iron frame attached to a mahogany pedestal. A set of two engraved plates showing the Large Lens, and a printed key describing its parts, are among BF’s papers at the APS. BF also received a handwritten table of 47 “Substances fused” with their weight and their time of fusion; a note on it indicated that some 300 more experiments had been made. This chart (also at the APS) showed that ten grains of platina fused in three seconds.
William Parker and Sons, glass manufacturers of Fleet Street in London, supplied Joseph Priestley with lenses and other glass articles needed for experiments: Robert E. Schofield, A Scientific Autobiography of Joseph Priestley (1733–1804) (Cambridge, Mass., and London, 1966), pp. 140–1, 367.
4. See RB to BF, May 20.