ON SEISMOLOGICAL INVESTIGATIONS. 53 



No slip of the Fault has been detected at present ; but we should 

 hardly expect a definite result during the short time in whicli the appa- 

 ratus has been in working order. 



The results obtaiued so far have been of use in pointing out the 

 difficulties to be overcome and the various defects of the instrument. 

 The movement of the ground caused by slight earthquakes and earth- 

 tilts is one of these difficulties, and our experiment on April 24 brought 

 this to light in a very striking manner. The instrument was placed at 

 the station SS. at the south end of the pipe/ and readings were taken 

 every few minutes from 1 to 3 P.M. These readings give the relative 

 movement of a tixed point in the strata and the surface of the oil. The 

 movement was most irregular, and during that time the maximum 

 displacement was about 0-3 mm. This can only mean that a line passing 

 through tixed points in the rock was constantly changing its angle with 

 the horizon ; and that the oil was always flowing backwards and for- 

 wards in its attempt to remain level. At about 1.40 p.m. the value of 

 the readings reached a minimum, and then began to increase, showing 

 that the angular movement of the strata changed its direction at this 

 time. If we assume that the oil was level when the two readings were 

 taken which differed by about 0-3 mm., it shows that the rock tilted through 

 an angle of about six and a half seconds. 



No doubt there vvas an exceptionally large movement due to slight 

 earthquakes and earth-tilts during the time that these observations were 

 being taken, as Mr. J. Milne tells me that his large pendulum at Shide, 

 Isle of Wight, was swinging regularly, and that this is supposed to be 

 due to earth pulsations. 



A telegram from Rome appeared in the daily papers reporting a slight 

 earthquake on April 24 at 3.30 p.m. at Lisbon, and a severe shock at 

 4.30 p.m. in Algarve, near Lisbon. (4.30 p.m. at Lisbon is 5.7 Greenwich 

 time.) 



A note appeared in ' Nature 'of July 18, 1901, saying that an account 

 of the earthquake of April 24 in the neighbourhood of Palombara Sabina 

 is given by Dr. Luigi Palazzo in the ' Atti dei Lincei,' x. 9. He thinks it 

 probable that the epicentre was at a sulphur spring about a kilometre 

 distant from Cretone, and that the origin of the shock was in the strata 

 from which the spring arises, at a comparatively small depth. Consider- 

 able damage was done at Cretone. The shock was registered at the 

 Central Meteorological Office at about 15h. 20m. 25s. Italian time : this is 

 2h. 20m. 25s. p.m. Greenwich time. 



Mr. Rollo Russell noticed an unusual agitation of the sea at 

 Bournemouth on April 24 at 7.50 a.m., and between 12 and 1 p.m. There 

 was also an exceptionally large wave soon after 3 o'clock.^ 



Mr. C. Davison '■ thinks that the disturbances may have been due to 

 the tiring of heavy guns. The disturbances were noticed in South Devon 

 and Guernsey as well as at Bournemouth, 



The movement of the earth on April 24 was no doubt exceptionally 

 large, but observations at other times lead me to think that such move- 

 ments, due to slight earthquakes and earth tilts, take place very frequently, 



' A lead pipe connects four vessels which contain oil ; they are in a straight line 

 at right angles to the Fault ; two of them are on each side of it at four and a half 

 and nine metres from it. 



■ See Aature, May 2, 1901. » Nature, June 6, 1901. 



