ON SEISM0L0G1CAI> INVESTIGATION. 261 



a system of levers from the bob of the latter, or from the weighted 

 extremity of the spring lever, a third pointer writes the vertical com- 

 ponent of motion side by side with the horizontal components. 



I particularly wish to draw attention to this type of instrument, 

 because I found it at several observatories, and it is a type that has 

 evidently found favour in the Italian Peninsula. 



For disturbances of short period it has no doubt been found effective, 

 but for the long rolling movements produced by earthquakes originating 

 at distances of 100 or 200 kilometres, when we have periods of from one 

 to foUr seconds, my own experience is that with such pendulums a more 

 or less violent swinging is established. 



The microseismoscope of (luzzanti consists of three inverted pendulums 

 of different periods arranged to make electric contacts. Should they be 

 set in a state of A'ibration, these contacts are recorded by an electric 

 magnet actuating a pen upon a moving band of paper. 



The Cecchi seismograph at Catania, as at other stations I visited, was 

 not in working adjustment, the reason for this being, I presume, that the 

 records from a Brassart type of instrument were found more satisfactory. 



Hanging against the wall of the same chamber with the large column 

 is a Bertelli-Rossi tromometer. This consists of a pendulum several 

 metres in length, a style from the bob or plummet of which is viewed by 

 a microscope with a micrometer scale. 



Another tromometer is that of Dr. Agamennone. This consists of an 

 ordinary pendulum with a multiplying lever, which actuates two small 

 mirrors, the movement of rays of light reflected from which are recorded 

 on a moving photographic surface. 



A very useful apparatus which I found here and at other observatories 

 is the photochronograph of Dr. Cancani, 



In a box attached to the wall is a chronometer, above which there is 

 a camera containing a plate and a small electric lamp. At the time of an 

 earthquake one or other of the seismoscopes on the great column make an 

 electric contact, which actuating an electric magnet turns on a current 

 for a second or so to the electric lamp. The result is that the face of the 

 chromometer is photographed. The last piece of apparatus to which ray 

 attention was drawn was a tide gauge-like recorder for a well. The 

 bottom of this well is, I understand, in the Pliocene strata beneath the 

 lava on which the observatory is founded. The depth is 32 metres, and is 

 9'5 metres above sea level. At the time of large earthquakes the puteo- 

 metric record shows that the water at that depth has been disturbed. 



Island of Isckla 



Until this year en the island of Ischia there have been two seismo- 

 logical observatories — one at the town of Ischia and the other at Cassa- 

 micciola. Dr. Grablovitz, the director of these stations, told me that 

 the former of these was to l)e abolished, and all the instruments brought 

 together at Cassamicciola. From the jetty at Cassamicciola you see the 

 observatory on the highest portion of a coUine some 300 feet above sea 

 level beneath the cliff- faced pinnacles of the extinct Epomeus. On reach- 

 ing it you look down upon the newly built houses and many ruins, which 

 testify to the disaster of 1883. 



The walls of the observatory, like those of the modern buildings, 

 instead of being built of stone and rubble, are of framed timber largely 



