Understanding the Fundamentals of Music (2006), by Robert Greenberg, B.A. in music (magna cum laude) from Princeton University, Ph.D. in music composition from the University of California, Berkeley. pp. 66-67 of the Lecture Transcript.
In 1815, a Viennese builder of mechanical instruments named Johann Nepomuk Maelzel patented a device he called a metronome (...)
(...) in 1873 Johannes Brahms, doing his level best to be absolutely crystal clear as to the moderately fast tempo of the third movement of his String Quartet, op. 51, no. 1, indicated that the movement should be played allegretto molto moderato e comodo, which means, literally, "very kind of, sort of fast, but moderately and leisurely." Does that make sense to any of you?
These quotes can be seen in the red line in the scan beneath. Why didn't Brahms mark with metronome markings?
Beethoven got himself a metronome and proceeded to write metronome marks into many of his works, including this third symphony.
The green line says that Beethoven did.