[LB063012], Letter from Thomas Alva Edison to Frank Loney Perry, February 1898
https://edisondigital.rutgers.edu/document/LB063012
Transcription
F.L.P. See "Loud Speaking Telephone" in Prescotts work on Elec & other works on telephony: This [illegible] apparatus is not only useful for telephone but for other things it has no “self induction” and would record alternating waves absolutelely true up to 100 000 per second — Yours Edison