96 REPORT— 1882. 



I learn from the ' Bulletino ' that in 1873 Professor Timoteo Bertelli, 

 of Florence, had published an historical account of small spontaneous 

 movements of the pendulum, observed since the seventeenth century up to 

 that time.' 



In 1874 (Anno 1 of the ' Bulletino ') Rossi draws attention to the 

 fact that there are periods lasting from a few days to a week or more, in 

 which the soil is in incessant movement, followed by a comparative cessation 

 of such movement. This he calls a 'seismic period.' In the midst or at 

 the end of a seismic period there is frequently a sensible earthquake. 



At page 51 he remarks, in a review of some observations of Professor 

 Pietro Monte (Director of the Observatory of Leghorn), that he was led 

 to suspect that the crust of the earth is in continuous and slow movement 

 during the seismic period, and that this movement is influenced by varia- 

 tions of barometric pressure. This suspicion was, he says, confirmed by 

 finding, in his observations of a pendulum at Rocca di Papa (of which 

 we shall speak again below), that during the seismic period the excursions 

 of the pendulum were mostly in the S.W. and N.E. azimuth. This is 

 perpendicular to the volcanic fracture, which runs towards the Alban 

 lake and the sea. The lips of the fracture rise and fall, and there result 

 two sets of waves along and perpendicular to the fracture. In an earth- 

 quake these waves are propagated with great velocity (the phenomenon 

 being in fact dynamical), but during the seismic period the same class of 

 changes takes place slowly. This view accords with observations at 

 Velletri made by Professor D. G. Galli. 



With regard to the influence of barometric pressure Rossi elsewhere 

 quotes M. Poey (October 15, 1857 ?) as having attributed the deviations 

 of the vertical to this cause, and remarks : — 



' Although he (Poey) gave too much weight to the baro-seismic action 

 of large variations of atmospheric pressure, yet after very numerous ob- 

 servations made by me in these last three years (I suppose 1871-4), I 

 can affirm that no marked barometric depression has occurred without 

 having been immediately preceded, accompanied, or followed by marked 

 micro-seismic movements ; but besides these there are other irregular, 

 often considerable and instantaneous movements, which occur under high 

 pressure. To distinguish them, I have called the first baro-seismic, and 

 the second vulcano-seismic, movements.' The reader will find a theoretical 

 investigation on this subject in the Appendix to the present Report. 



Rossi states (page 118, Anno 1 ?) that whilst Etna was in a condition 

 of activity his pendulums at Rocca di Papa were extraordinarily agitated 

 at the beginning of each barometric storm. 



At page 90 of the second year are given graphical illustrations of the 

 simultaneous deflections of pendulums at Rome, Rocca di Papa, Florence, 

 Leghorn, and Bologna. There is some appearance of concordance between 

 them, and this shows that the agitations sometimes affect considerable 

 tracts of land, but that the minor deflections are purely local phenomena. 



M. d'Abbadie, in presenting a memoir on micro-seismic movements 

 by Father Bertelli to the French Academy, relates (' Comptes Rendus,' 

 1875, vol. 81, p. 297) the following experiment made by Count Malvasia, 

 as proving the independence of the disturbances of the pendulum from 

 the tremors produced by traffic. Two batteries of artillery were marching 



' Bulletino Soncamj>affni, t. vi. Gennaio, 1873. Eeprinted Via Lata, No. 2114, 

 Kome. 



