ON SEISMOLOGICAL INVESTIGA.TIO-\. 263 



in length, and therefore multiply any motion of the tray nearly 100 

 times. Their outer ends carry writing points, resting against the face of 

 a drum, driven by clockwork. To prevent these pointers following the 

 same line as the drum revolves a cylindrical sinker is gradually lowered 

 by means of clockwork into the water. The water therefore gradually 

 rises, and with it the floating tray, and the writing levers gradually 

 change their position on the recording surface. Tiie natural period of 

 this tray when set in oscillation is about one second. 



The geodynamic levels consist of two zinc tubes, each 2-5 metres in 

 length, terminated at each end with vertical cylinders. These stand on 

 the floor of the room at right angles to each other. On the open ends of 

 these there are floats attached to the short arms (each 8 mm. in length) of 

 levers. The long arm of each lever (80 cm. in length) carries a writing 

 pointer, resting on a recording surface moved by clockwork. The 

 natural period of these water levels is 2 '5 seconds. 



(For further description in English and reference to original descrip- 

 tions see Report of the British Association, 1896, p. 226.) 



These instruments give an exaggerated representation of the pre- 

 liminary, and therefore fairly rapid, vibrations of an earthquake origi- 

 nating at a great distance, whilst they show but little of the succeeding 

 slower but larger waves. The general character of their records is there- 

 fore the reverse of what is usually obtained from a horizontal pendulum. 



The chief instrument at Porto d' Tschia, a few miles distant from 

 Cassamicciola, is a pair of horizontal pendulums. The vertical height of 

 these is 2 metres. The weights, which are 12 kilos., are carried on booms, 

 10 cm. in length, supported by double ties, one from each side of the 

 weight, but coming together at a point at their attachment above the 

 pivot of the boom. The object of this is to prevent wobbling. The boom 

 is prolonged 80 cm. to its hanging writing point, which rests against a 

 smoked surface of paper moving at a rate of 1 cm. per minute. 



Rome, 



The Ufficio Centrale Meteorologico e Geodinamico Italiano, ^^•hich forms 

 portion of the Collegio Romano, is a huge block of buildings surrounded 

 by streets, which stands back al)out 40 yards from the Corso, one of the 

 principal thoroughfares in Rome. The effect of the traffic is extremely 

 .slight, and only occasionally to be observed. Here I met Professor P. 

 Tacchini, the director-in-chief of the meteorological and seismological 

 work of Italy, who very kindly explained the general working of the 

 departments, showed me the instruments, and indicated how I could 

 obtain materials I might require. 



One of the upper rooms is devoted to the storing of seismological 

 records and their analysis. When an earthquake occurs in any portion 

 of Italy the observers in the shaken district fill up a postcard-like form 

 and forward the same to this bureau. If the shaking was confined to the 

 island of Sicily, then some thirty of these forms would be received, 

 whilst if it were in the peninsula some hundreds might come in. 



A digest of this information, together with many detailed observations 

 from stations provided with seismographs, is from time to time published 

 in the ' Bollettino della Societa Sismologica Italiana.' Fuller accounts of 

 observations and instruments appear in the ' Annali dell' Ufficio Centi'ale 

 Meteorologico e Geodinamico Italiano' (see vol. viii. Part IV. 1886). 



