[LB059241], Letter from Thomas Alva Edison to Frederick Perry Fish, December 15th, 1896
https://edisondigital.rutgers.edu/document/LB059241
Transcription
Decr 15- 1896 Friend Fish- I intended to come over and see you today but had to go up to the Mine which is running ie the Briquette part, and with great success, in the course of two or 3 months I shall have the whole running full and then can give more time to other things = I have arrived at a very curous stage in the lamp filament work which is this = I had worked the filament up so that at 23 per horse power the life is closely on 200 hours which should give 600 to 800 hours at 20 per hp & several thousand hours at [illegible] per 15 per hp the present economy - Howell came up and said that the Co wanted a good 8 cp lamp & I said I would set up one of my new lamps (16 cp 375 c per hp) at 8 candles (or 240 c per hp) I did so & found that the life was less at 8 than at 16 ie the higher the Cp the better the life, several sets were set up and this is the case. Evidently I have a perfect filament & am now working on vacuum – will write you further as I have now to get train Yrs Edison