GEOLOGY. 287 



PHENOMENA ATTENDING THE EARTHQUAKE IN CHILI, APRIL, 1851. 



Lx. GILLISS, in charge of the U". S. Astronomical Expedition to Chili, 

 furnishes to the National Intelligencer, Washington, the results of the 

 observations made on the great earthquake which occurred April 2d, 

 1851, at Valparaiso. He says : " The instrument for measuring the 

 direction and comparative violence of earthquakes, brought with us, 

 having failed to record any of those previously occurring, in December 

 last I caused a pendulum nine feet ten inches long to be made, with 

 its lead ball, and some fine silver wire suspending the pendulum from 

 a tripod. A common needle is inserted in a cork at the bottom of the 

 ball, which just touches a sheet of glazed paper marked with concen- 

 tric circles and the points of the compass. The paper lies on a hori- 

 zontal plate of glass resting on the earth, and is sprinkled with black 

 sand, so that the motion of the pendulum leaves a white line exposed. 

 It is to be regretted that the paper had not been secured to the earth, 

 for during the shock there was a displacement bodily of about half an 

 inch ; but we have a distinct ellipse, whose diameters are 3.5 in. and 

 2.4 in., and positive evidence that the motion of the disturbing force 

 was in a line varying little from N. by E. to S. by W., or contrary to the 

 supposed direction in which the earth-wave has moved in all preceding 

 great disturbances. Having personally traced the effects of the shock 

 along its eastern line as far south as Rancagora, and also a section 

 across the axis of motion to Valparaiso, no doubt remains on my mind 

 that there are local causes (as the geological formation) which influ- 

 ence both the direction and violence of the phenomenon to a very great 

 extent. At Valparaiso the direction from which the shock came was 

 near N. E. by N. ; though the opinion among the masses is that it came 

 from the opposite quarter. There is no indication that the land has 

 been elevated in any part of the bay. For several days before and 

 after there were extraordinary fluctuations of the barometer, and 

 overcast weather." 



PRESENT CONDITION OF VESUVIUS. 



THE eruption of Vesuvius in February, 1850, and that of the year 

 previous, entirely changed the summit features of this ancient mountain 

 of fire. The former crater disappeared, being filled with scoria and 

 ashes, while two craters now occupy the summit of the cone. The 

 deepest and most active of these is that of February, 1850, which is 

 situated on the side of the cone nearest to Pompeii. It is somewhat 

 lower and has a much greater depth than its immediate neighbor, 

 which is on the side of the bay of Naples. We had no means of meas- 

 uring its depth accurately, but judging from the time required for the 

 returning sound of a stone cast into its mouth, as well as from inspec- 

 tion and comparison, we assumed the depth of the new crater to be 

 from 800 to 1000 feet. It is acutely funnel-shaped, at an angle of not 

 less than 60. It is impossible, because of the steam and vapors of sul- 

 phurous acid, to see its bottom, even if not prevented by the danger of 

 the descent to a position where one might hope to catch a glimpse of 



