[LB039169], Letter from Thomas Alva Edison to Edison Machine Works, Samuel Insull, March 24th, 1890
https://edisondigital.rutgers.edu/document/LB039169
Transcription
Orange, N.J. March 24, 1890 Samuel Insull, Esq., Gen'l Manager, The Edison Machine Works, #44 Wall St., New York City. Dear Sir:- I have your letter of 22nd instant, enclosing extract from a letter received by you from Mr. Ward Leonard, with relation to carbon brushes, and in reply would say that I am very much opposed to the use of these brushes, except where it is actually necessary. Good copper brushes with fair attention are the best that can be devised; but, where no attention can be given and load suddenly varies, or where there are ignorant, careless attendants then carbon ought to be used. I have always stated that instead of carbon the German silver connection-wire between commutator and abature is the most perfect device known to stop sparking when load varies. Yours very truly, Thos A. Edison