PHYSICS OF THE GLOBE. 105 



tive; and Cotopaxi, in Eqnador, was in eruption at the same 

 time. 



On October 4, 1878, at 2 30 A.M., a shock sufficient to move 

 furniture was felt in the valley of the Hudson River. 



Observations by Professor Palmieri and others during Sep- 

 tember and October, 1878, indicate an approaching eruption 

 of Vesuvius; but it progresses slowly, and, though ejecting 

 flames and lava, had, up to December 1, done little damage. 



TERRESTRIAL MAGNETISM. 



John Allan Broun has compared the curves representing 

 the mean ranges of the diurnal oscillations of the magnetic 

 needle for the last three minimum epochs, viz., 1856, 1866, 

 and 1876, showing that in the first of these the minimum is 

 strongly marked, in the second not so clearly, while in the 

 last the minimum period extends over more than two years- 

 and inferring therefrom that we are now passing through 

 a long minimum period similar to that which occurred at 

 the close of the last century (Nature, vol. xvii., pp. 183, 259, 

 280). 



Both Mr. Broun and Balfour Stewart have compared the 

 cycles of declination ranges, and of sun-spots, and confirm 

 the generally received opinion of a close accordance ; the 

 latter, however, finding, with the same length of period, a 

 lagging of the magnetic epoch behind that of the sun-spots, 

 amounting in one case to five months. They agree in 

 attributing the two sets of phenomena to a common cause 

 (Nature, vol. xvii., pp. 262, 326). The same subject is dis- 

 cussed by Joas Capello (Nature, vol. xvii., p. 488), and by 

 M. Faye in the Annuaire of the Bureau of Longitudes for 

 1878; the latter finding in the sun's heat a cause for the 

 phenomena. 



Mr. Broun discusses M. Faye's paper, mentioned above, 

 giving reasons for opposing his view that the diurnal oscil- 

 lations of the needle are caused by solar heat ; urging es- 

 pecially that there is no evidence of any decennial change 

 in the solar heat which bears to the M'hole amount any 

 such proportion as the decennial magnetic variation bears 

 to its whole amount (Nature, vol. xviii., p. 126). 



Mr. Broun also shows that the moon produces a variation 

 in the earth's magnetism such that the needle makes two 



E2 



