Cecchi's instrument has been described by some as the first true seismograph.
The record (seismogram) obtained by a Cecchi seismograph at Moncalieri, Italy, on February 23, 1887
USGS
Cecchi's seismograph was built in 1875. It was designed to record the relative motion of a pendulum and the Earth as a function of time. For horizontal vibrations, two common pendulums were used, one vibrating in a north-south plane and the other vibrating in an east-west plane. The pendulums "beat seconds"; their motion was magnified three times by a thread-and-pulley apparatus. For vertical motions, a mass on a spiral spring was used. A machine that recorded rotary motions, was incorporated into the seismograph. This consisted of a cross bar with weights at both ends, much like a dumbbell, which was pivoted at its center of mass so as to rotate in a horizontal plane. Restoring force was applied to the dumbbell by springs, so that it oscillated with a period of one second.
Cecchi arranged a seismoscope to start a clock and to start into motion the recording surface at the time of an earthquake. The recording surface would translate under the indicating needles at a speed of one centimeter-per-second for twenty seconds. From the time on the clock, an observer arriving at the seismograph would determine how long before his arrival the earthquake had occurred.
Cecchi's instrument was apparently installed in several observatories. Tbe earliest date found for a seismogram obtained with a Cecchi instrument is February 23, 1887, when one of these seismographs recorded a large earthquake which occurred in the French-Italian border region. In that earthquake, only the east-west component was recorded, although the seismograph was located in a zone of strong shaking. However, the seismogram record appears to us to be as accurate a representation of earth movement as possiible by an early seismograph.
