[D8621L], Letter from Thomas Alva Edison to Edward Hibberd Johnson, November 21st, 1886


View document with UniversalViewer   → View document on Archive.org  → Re-use this digital object via a IIIF manifest


[D8621L], Letter from Thomas Alva Edison to Edward Hibberd Johnson, November 21st, 1886

Editor's Notes

[Long, technical letter handwritten by TAE, with multiple illustrations in regard to Municipal system. Gives series of ideas on how to structure a lamp cut off.] Yours re municipal received just in time to answer by mail today. I will think it over further but think I can give you what you want. Here is the rough idea. Ask John Ott to let Hamilton make the mixtures for you. ##Note: Ordinary charcoal does not conduct to any appreciable extent. The conducting power of charcoal depends up to a certain limit to the temperature it is brought when first carbonized. [Describes why charcoal will therefore not work as a conductor and how to make it a better conductor, and says Upton can make him a type of charcoal stick that will have an even resistance. Discusses what would happen if put a piece of charcoal across wires, with sketch.] "Another way would be to powder, as you suggest. Tamp it in and then put a wad of asbestos etc. to hold it well tamped. Then with a large body it would come down to a very low resistance. ##Ordinary Lampblack is also a practical non conductor. There are various qualities of varying resistances. This should be tried." [Discusses how to make a mixture of lamblack and oxide of magnesia to create varying resistances and what the results would be. Concludes that "The resistance of this compound would probably never come down so low as to act as a cut off itself like the piece[?] of charcoal."] [Lists substances that are partial conductors, with some notes on many of them.] [Series of sketches showing possible ways to use anthracite; also describes how anthracite resistance is changed. Then discusses how mixing lampblack with protoxide of lead could work as a cut off. "The oxygen of the lead unites with the carbon and metallic lead is instantly formed."] ##Note: No amount of lead in glass makes it conduct as the lead is in the form of an oxide and is a non conductor." ##Here is an idea [Sketch of light with contraption next to it, then description of how it could use "a moulded material having a stiff gum like licorice, sealing wax, asphalt, etc., mixed with conducting lampblack so it have say 5000 resistance." Discusses how that would work.] ##"I'm getting short of ideas and mail is closing. Will send some more soon. God bless you, my boy. Amen in haste."
Supplied month




Folder/Volume ID


Microfilm ID


Document ID



Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
Download CSV | JSON