ON THE VOLCANIC PHENOMENA OF VESUVIUS. 227 



rainfall, together with the phases of the moon, deduced from observations 

 extending over two years. The method of registering the different 

 degrees of activity ' is that described in the report of this Committee last 

 j-ear. The results seem to indicate a distinct relationship between 

 barometric pressure and the violence of the explosions, or, in other 

 words, the ebullition of the lava. On the contrary, the rise and fall of 

 lava level within the chimney in relation to tidal action set up within 

 the magma is doubtful, though some coincidences are remarkable. The 

 short time during which observations have been carried on, and the 

 facility with which any true rise and fall of lava may be masked by other 

 causes, necessitates the study of the subject for some years longer. 

 Observations during the past fourteen months go to confirm the conclu- 

 sions arrived at in the paper above mentioned. 



The fourth sheet of the geological map of Monte Somma and 

 Vesuvius has been completed, and is exhibited at the meeting. Although 

 small — a good portion being sea — much patience and time were necessary, 

 owing to the area being thickly inhabited and the ground broken up by 

 numerous small gardens, &c., enclosed within high walls. The geology 

 of the region mapped in this sheet is slightly more difficult to work out 

 than that included in the third sheet (exhibited at the last meeting), 

 and is much more intricate in detail. Sheet 5 is in considerable part 

 mapped, and the reporter had hoped to have completed it for exhibition 

 at the present meeting beside Sheet 4, but he was prevented by a 

 number of family troubles, which forcibly diverted his attention during 

 the spring and early summer. The reporter regrets to announce that 

 the ' Giornale del Vesuvio,' containing a diary of all the observations 

 made during the last four years, and which should have appeared eight 

 months ago, is not yet published. This delay, however, is not the fault 

 of the author. Proofs of nine of the illustrations in phototype are 

 exhibited at the meeting. 



The present year is remarkable for the chances it afi'ords for 

 studying the subterranean structure of the Campi Phlegrei and the 

 volcanic region around Naples. The great main drain, which is to convey 

 the sewage of Naples to the Gulf of Gaeta, will traverse the region west 

 of Naples on a line running nearly east and west. Before, however,, 

 oonstructing this sewer a series of five borings have been made to test 

 the ground to be cut through. Observations on the water level, tem- 

 perature, and presence of volcanic gases were made. Although these 

 borings in themselves have brought no remarkable fact to light, they 

 will, combined with the deep artesian well at Lago Fusaro, form 

 important documents for the study of the structure of such a complicated 

 region. 



Five other borings on or near the renowned Starza or foreshore of 

 Pozzuoli, on the works of Sir W. Armstrong, Mitchell, & Co., are in- 

 teresting as being within a few hundred yards of the celebrated so-called 

 Temple of Serapis. Details of these, two of which are on the beach and 

 the other three at varying distances out to sea, will be published together 

 with others being made. For the present, however, it may be said that 

 these borings fully confirm the opinions generally held as to the oscilla- 

 tions of the ground in this district. 



' And not of the quantity of vapour, as erroneously stated in the Abstract, Proc. 

 Roy. Soc. No. 243, 1886. 



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