Earthquakes (not of a violent character within recent centuries, though the ruin of the Colosseum is probably to be ascribed to this cause) are not unknown even at the present day in Rome and in the Alban Hills, and a seismograph has been established at Rocca di Papa.
South-east of the walled city, the number of perceptible earthquakes registered by seismograph between 1880 and 1897 inclusive was 221; the greatest numbers for any one year were 26 in 1882 and 23 in 1892, and the least, 5 in 1896 and 6 in 1889 and in 1894; the average number in each May was 1.44, in each July, 1.33, and in January and in February 0.72; the frequency is much greater in each of the spring summer months (except June, average 0.78) than in the months of autumn and winter.
For local earthquakes it will move relatively to the pivoted balance weight like an ordinary bracket seismograph, and for very rapid motion it gives seismoscopic indications of slight tremors due to the switching of the outer end of the boom, which is necessarily somewhat flexible.
The Strassburg or Bosch seismograph differs from those just described in resembling the Milne instrument, it is a horizontal and not a vertical pendulum.
The Galitzin seismograph, devised by Prince Galitzin, is of the same type, but it essentially differs from the Milne instrument in having its pendulum dead-beat; this is brought about by an electromagnetic device.