In a message dated 7/12/01 12:27:44 AM GMT Daylight Time, tedr@.................. writes: << There was also a complicated mechanism between the end of the arm and the stylus, time did not allow me time to work out what did but it obviously had a use. The question I ask is: was it a Lehman and if so why hang the mass half way along and below the beam? Is it to magnify the amount the weight apparently moves??? And how were the oscillations damped, if indeed they were. >> Hello Ted, My first seismograph recorded with pen and ink on paper. I consider this now obsolete recording method much more satisfying than writing with an electron beam on a computer monitor, which I now do. I am therefore very interested in the museum's ink on paper seismograph and here are my best guesses as to how it works: 1) No, I don't think it's a Lehman. What you see as a Lehman boom is probably a support arm for a 12-inch long hanging-mass pendulum swinging from half way out on the support arm. 2) You describe what looked like: "a complicated mechanism between the end of the arm and the stylus". My guesss is this is a mechanical amplifier, a system of levers that causes the pen to move much farther than the amount the Earth moves in relation to the suspended mass, when the device records an earthquake. 3) A careful designer could design such a system of levers to give perhaps anywhere from 20 to 50 X magnification of actual Earth movement due to an earthquake. With such a mechanical advantage the pen itself sliding on the paper would probably provide sufficient damping. In a later posting, Chris Chapman says: "I live 50 miles away, but I plan to visit it in the next two months, if that is any help." I hope Chris will take a camera along and talk nice to the museum director so he will be allowed to take some close-up pictures of the "complicated mechanism" so we can figure out what it does and how it does it. Best regards, Cap __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>