In 1877, Francis Blake invented a carbon microphone for use in the telephone, and patented it before Thomas Edison invented a similar microphone that also used carbon contacts. Blake used a carbon button design that initially would not stay in adjustment, but with later improvements proved to be workable. Alexander Graham Bell hired Blake and put him to work with Emile Berliner who also invented a carbon microphone. The improved Berliner-Blake microphone was standard with the Bell company for many years.
Blake worked on the United States Coast Survey from his teenage years through early adulthood (1866-1878). He was a physicist and an amateur photographer.
In 1874, Blake married Elizabeth Livermore Hubbard (1849-1941) whose father provided land in Weston, on which Blake designed and built an elaborate house where he conducted his electrical experiments. They had two children: Agnes (Blake) Fitzgerald (b. 1876) and Benjamin Sewall Blake (b. 1877).
He died at his home in Boston on January 20, 1913.