The Early History of Seismometry (to 1900)

by
James Dewey and Perry Byerly

Seismoscopes in Eighteenth Century Europe

We find Europeans writing on earthquake-detecting instruments from the early eighteenth century. In 1703, J. de la Haute Feuille proposed filling a bowl to the brim with mercury, so that an earthquake would cause some of the mercury to spill out (de la Haute Feuille, 1703; Favaro, 1884). In order to determine the direction of the shock, the mercury spilling out in each of the eight principal directions of the compass was to be collected in cavities or other containers. In an earthquake, de la Haute Feuille assumed, the ground would be inclined, and the direction in which the mercury spilled would be away from the origin, "where the ground began to be raised" (Favaro, 1884, p. 95). It is interesting that this earliest of European instruments was expected to respond to tilting of the Earth's surface rather than to horizontal displacements. An indication of the distance of the epicenter and the size of the disturbance could be had from the amount of mercury which had sloshed out.

An important function of de la Haute Feuille's instrument was to provide data from which future earthquakes might be predicted. His proposed method of earthquake prediction was to use his instrument to record the small shocks which he supposed must precede a large earthquake. Each day, an observer would note the amount of mercury spilled out of the bowl, if any had been spilled. If a large amount of mercury spilled out, a large earthquake would probably be imminent. With a large body of observations, patterns might be detected which would enable the prediction of future earthquakes. De la Haute Feuille seemed to believe that earthquakes were caused by the explosion of sulphurous matter and various salts within the Earth. Davison (1927) has indicated that this idea was widespread in de la Haute Feuille's time.

De La Haute Feuille clearly understood that instruments would make an important contribution to seismology. He emphasized the need for large numbers of instrumental observations in order to learn about earthquakes. Nevertheless, there is no evidence that his seismoscope was ever built. De la Haute Feuille's suggestion seems to have had little influence on the development of seismometers. A closely similar instrument was built in 1784 by A. Cavalli, probably without knowledge of de la Haute Feuille's writing (Baratta, 1895, p. 8).

The honor of being the first European to record the use of a mechanical device as an aid to the study of earthquakes goes to Nicholas Cirillo (1747). Cirillo employed simple pendulums in an investigation of a series of earthquakes in Naples in 1731. He observed the amplitude of pendulum oscillations at the locations where the shaking was most severe, and also at locations somewhat removed from the zone of severest shaking. He found the amplitude to decrease with the inverse square of the distance, a result he anticipated from "the common laws in other sorts of motions" (Cirillo, 1747, p. 682).

In 1751, Andrea Bina proposed suspending a common pendulum, with a pointer attached to its lower end, above a tray of fine sand (Bina, 1751). The relative motion of the pendulum bob and the Earth was to be traced in the sand by the pointer. Bina seems to have built his instrument, but we do not know if an earthquake was ever recorded with the device. Bina's instrument was intended to tell the observer the character of the ground motion. The nature of the record traced in the sand would reveal whether the earthquake motion was "regular or swaying ..., tremulous or irregular..." (Bina, 1751, p.46).

The construction of instruments in eighteenth-century Italy frequently coincided with periods of unusually high local seismic activity. The Calabrian earthquakes of 1783 were responsible for the greatest surge of interest. Davison (1936) lists six "principal" earthquakes in this series of shocks. Loss of life and property was enormous. The earthquakes were the subject of several detailed investigations, including a study by the first appointed "Earthquake Commission" (Davison, 1927, p. 29). The use of mechanical devices to verify the occurrence of earthquakes seems to have been natural to people living in areas affected by these shocks. Salfi (1787, p. 46) reported that the general populace used liquid-filled bowls and delicately-balanced objects as seismoscopes.

The shocks also spurred the invention of more elaborate instruments. The most complete treatment of these instruments is given by Baratta (1895), who reproduces important sections of the original papers. Lacking some of the original papers, we have relied heavily on Baratta's study and the portions of the originals reproduced therein.

D. Domemico Salsano, a clock-maker and mechanic of Naples, invented a "geo-sismometro" in February, 1783 (Salsano, 1783). It was operating shortly after the first large Calabrian earthquake. It was a common pendulum, eight and a half "parisian" feet long. The pendulum mass was equipped with a brush, which was to record the motion of the mass with slow-drying ink on an ivory slab.

Reports of the observations made by Salsano (Salsano, 1783; Torcia, 1784) suggest that his pendulum may have responded to some of the earthquakes in Calabria, about two hundred miles away. The nature of the recorded observations suggests that many motions of the pendulum were not due to earthquakes, as might be expected for a pendulum in an unsheltered location. Nevertheless, sometimes the pendulum motions were roughly contemporaneous with earthquakes in Calabria. We are not told how exactly the pendulum motion and the earthquakes coincided in time. It is clear also from the description of observations that most, it not all, of these observations were made by watching the pendulum, rather than by examing records written by the pendulum. The pendulum was arranged to ring a bell when its oscillations were large enough. This it did on several occasions.

Salsano's seismoscope received relatively little mention in the large studies of the Calabrian earthquakes. Baratta notes that some who did refer to the machine treated it with scorn. One writer, F. Salfi, pointed out that the instrument was nothing more than an ordinary pendulum, and criticized those who would "push to the foot of the throne" the merits of its inventor (Salfi, 1787, p. 46). Salfi's statement, however, hints that Salsano's instrument was well known in its time, in spite of the lack of printed recognition. Later, during the New Madrid earthquakes of 1811 and 1812 in America, Daniel Drake of Cincinnatti reported the used of an "instrument constructed on the principle of that used in Naples, at the time of the memorable Calabrian earthquake" which reportedly "marked the direction of undulation from south-southwest to north-northeast" (Fuller, 1912, p.27). Baratta (1895) also mentions a common pendulum constructed by Zupo, which wrote in sand. Perhaps this was the Neapolitan instrument to which Drake referred.

In the years immediately following the Calabrian earthquakes, two other seismic instruments were described which should be mentioned here. A. Cavalli, in 1784, reinvented de la Haute Feuille's mercury-filled-bowl seismoscope (Cavalli, 1785). In addition, he designed a modification of this instrument which would give the time of an earthquake, to the nearest minute. This was to be accomplished by the use of platforms rotating beneath two mercury-filled bowls. As the platforms rotated, cavities corresponding respectively to the hour of the day and the minute of the hour would pass beneath the notches in the sides of the bowls. When mercury overflowed from the bowls through the notches, it would be conveyed into the two cavities corresponding to the hour and minute of the day. The observations reported by Cavalli suggest that the time-telling part of his seismoscope was never built (Cavalli, 1785). This instrument, if it was constructed, was the first designed to tell the time of an earthquake.

The Duca della Torre, A. Filomarino, invented a common pendulum "sismografo", similar to Salsano's, but with the addition of a time-telling device. The first known description of this instrument is from 1796 (della Torre, 1796), although Salsano (1783) mentioned an instrument similar to his own, which he had not seen, invented contemporaneously by Duca della Torre. A record was to be written by a pencil attached to the pendulum and pressed gently with a spring against a piece of paper. On the pendulum mass was to be put a hair, which would arrest the balance wheel of a clock. When the mass moved, the hair would be withdrawn and the clock would start.

Several written records were observed with this instrument. The records consisted of a pencil-line or two for each earthquake. They must have contained little more information about earthquake motion than could have been obtained from "natural seismograms", such as scratches left by a heavy object moving on a smooth surface. Nevertheless, the Duca della Torre is the first to describe a record obtained with an instrument constructed as a seismometer. The observations given by him, as reproduced by Baratta (1895, p. 31) do not suggest that the timing device was functioning.

From the Bulletin of the Seismological Society of America. Vol. 59, No. 1, pp. 183-227. February, 1969.