ON SEISMOLOGICAL INVKSTIGATIOX. 265 



At the doorway you stand 760 metres above sea level on a boss of leucite- 

 basalt, the nucleus of a once extensive crater. Looking down, you see the 

 roofs and gardens of Rocca di Papa beneath, towards the left is the 

 crater lake of Albano, and towards the right the villages and towns which 

 dot the Carapagna, Rome with its St. Peter's, domes and towers, and in 

 the far distance the Mediterranean. There is nothing above you, and 

 you see homesteads and hamlets, with here and there a town below as in 

 a plan. 



The first thing to be noticed is that the observatory, although built of 

 stone, is covered with galvanised iron sheets. The object of this is to- 

 prevent the absorption of moisture, which in consequence of mist and an 

 annual rainfall, which at this elevation exceeds one metre, would be 

 excessive. 



An ascent up a few steps takes the visitor through glass doors, which 

 are opened by a custodian in official uniform, into a lofty, well-lighted 

 octagonally-shaped room about 8 metres in width. From the basement a- 

 column of masonry 6 metres in diameter rises up to the floor of this room, 

 where it is continued upwards into the room itself as an annular table 

 about 3 feet in width and 3 feet in height. This, which is faced and 

 covered with white marble, carries about twelve instruments. 



In the centre of the annular si^ace a circular column 1"25 metre in 

 diameter rises nearly to the roof of the building. I understood that the 

 object of this was to study the behaviour of certain instruments placed near 

 its top as compared with that of similar instruments placed at lower 

 levels. 



At the time of my visit five seismoscopes were installed on small 

 shelves attached round the summit of this shaft. These are electrically 

 connected with a Brassart seismograph, and when one or any of them are 

 agitated the recording surface connected with this apparatus is set m 

 motion. Experience shows that seismoscopes installed upon the top of 

 this elastic column move sooner than similar apjaai-atus placed upon the 

 circular desk. 



Hanging round the sides of the column are a series of tromometer.s^ 

 varying in length from about 15 feet to 6 inches (see description of the 

 Catania tromometer). At the present time I believe it is only thi^ 

 longest and shortest of these which are observed, records being taken five 

 times daily. 



On the circular table there are a lar^■e number of seismoscopes, including 

 the original designs of Professor 31. S. di Rossi,' Brassart's Seismograph, 

 and the Photo Chronograph of Dr. Cancani. 



At this observatory there is another example of the long pendulums; 

 It is 15 metres in length and carries 250 kilos. The multiplication is, as at 

 Catania, 12*5 times, and the record is with ink. On tJie opposite side o€ 

 the room and hanging from the wall is a Vi(.-entini pendulum, which will' 

 be described with the instruments I saw at Padua. 



Among the most striking pieccss of apparatus at this observatory are a 

 pair of horizontal pendulums constructed by Dr. Cancani, which of their 

 kind are the largest in existence. The height of the vertical axis is 5-25 

 metres (17 ft.), and the length of the horizontal boom is 2'7 metres 

 (8 ft. 9 in.). Each pendulum is constructed from two pieces of T-iron 

 brought together and joined to form two sides of a triangle. The free 



' See Za Meteorologia Endogena, vol. ii. 



