347 



mate orbit. They were made principally with the author's equatorial 

 telescope, having a focal length of 25 feet 3 inches, and a clear aper- 

 ture of 13*3 inches. Some few, however, were taken with the finder, 

 which is 6 feet 6 inches in focal length, and 4*9 inches clear aperture. 

 The eye-pieces used were, one by Frauenhofer (an illuminated wire- 

 micrometer), one by Messrs. Troughton and Simms (an illuminated 

 field-micrometer), a comet eye-piece, and the ordinary eye-piece of 

 the finder. The first of these had a magnifying power of about 400, 

 the second of 226, the third of about 95, and the fourth about 40. 



(( An Account of the great Earthquake experienced in Chili, on 

 the 20th of February 1835," with a Map. By Alexander Caldcleugh, 

 Esq., F.R.S. 



An idea formerly prevailed among the inhabitants of Chili, that the 

 earthquakes of those regions take place at certain regular periods j 

 but it is now sufficiently proved, from the numerous catastrophes of 

 this kind which have occurred during the present century, that they 

 may happen indiscriminately at all times, and in all states of the at- 

 mosphere. The author is disposed to place but little reliance on most 

 of the supposed prognostics of these convulsions : but he mentions 

 that, previously to the earthquake described in the present paper, there 

 were seen immense flocks of sea birds, proceeding from the coast to- 

 wards the Cordillera, and that a similar migration had been noticed 

 prior to the great shock of 1 822. From his own observations, he con- 

 cludes that the barometer usually falls shortly before any considerable 

 shock, and that it afterwards rises to its ordinary mean height. Both 

 before, and also at the time of the convulsion, the volcanos of the 

 whole range of the Cordillera were observed to be in a state of extra- 

 ordinary activity. 



The earthquake began at half-past eleven o'clock in the morning 

 of the 20th of February. The first oscillations of the earth were gen- 

 tle, and attended with little noise : they were succeeded by two ex- 

 tremely violent tremors, continuing for two minutes and a half, the 

 principal direction of the motion being from south-west to north-east ; 

 and they were attended by aloud report, apparently proceeding from 

 the explosions of a volcano to the southward. All the buildings of 

 the town of Conception were thrown down during these undulations. 

 At the expiration of half an hour, when the inhabitants, who, on the 

 first alarm, had fled to the neighbouring heights, were preparing to 

 return to their houses, it was observed that the sea had retreated to 

 such a distance that the ships in the harbour were left dry, and all 

 the rocks and shoals in the bay were exposed to view. At this pe- 

 riod an immense wave was seen slowly advancing towards the shore, 

 and, rolling majestically onwards, in ten minutes reached the city of 

 Conception, which was soon overwhelmed in a flood of an altitude of 

 28 feet above high-water mark. The few persons who had remained 

 in the town had but just time to make their escape, and to behold from 

 the rising grounds, the complete submersion of the city. All objects 

 that were movable were swept away into the ocean by the reflux of 

 this great wave, which was succeeded by several similar, but smaller 



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