AT TWENTY-ONE STATIONS IN EUROPE. 91 



In this table the mean time of the oscillations at Paris and the mean of the 

 observed dips in 1837 and 1838, is taken as the unit of reference in calculating 

 the relative horizontal and total intensities. 



The total intensity at Trieste, compared with Paris, is given by Major Sa- 

 bine, in his report before referred to, as determined by Messrs. Keilhau and 

 BoECK, in 1826, as 0.977; differing from the mean of my results 0.007, the 

 difference betvi^een us having a contrary sign from that at Vienna. M. Que- 

 TELET* gives the horizontal intensity at Venice as 1.1566, which is much 

 greater than my number. 



ROME AND NAPLES. 



The observations at Rome were made at two different stations; one out of 

 the region of the volcanic tufa upon which the city is built, upon the calcare- 

 ous formation of Monte Mario, in the garden of the Villa Mellini, the other 

 in the temple of Venus and Rome, opposite to the Colosseum. At the latter 

 station a curious instance of local attraction occurred: I had selected a block 

 of marble, apparently free from iron fastenings of any sort, as the resting place 

 for the instrument, and finding results very discordant from those obtained on 

 the Monte Mario, I next placed the instrument in a brick niche, to examine if 

 the local attraction were common to the whole station. The results obtained 

 when the instrument v/as in the niche were so different from the former that I 

 placed it again upon the block, to ascertain if any mistake had occurred, but 

 found again the same anomaly as at first. There was, probably, some iron be- 

 neath the pavement upon which the block of marble rested, suggesting the ne- 

 cessity for caution in the selection of these places of observation. 



Fearing the influence of the ferruginous nature of the volcanic tufa upon 

 which Naples is built,t I went to Aversa, about eight miles to the north of the 

 cit3^ The place of observation was in the large garden attached to the Asy- 

 lum for the Insane. 



* Amiuaire de I'Observatoire de Bruxelles pour I'an 1834. 



1 1 certainly did not at that time remember that M. Quetelet had expressed his opinion that 

 there was no local disturbance from this cause, or I should have deferred to his authority. Never- 

 theless, the preoaution, though attended with some inconvenience, was not amiss. 



