EARTHQUAKES. 127 



and its western face is precipitous and nearly vertical, almost without a foothold for vegetation. 

 Our observatories occupied u platform made by breaking down the rock near the northern limit 

 of the crest, and 175 feet above the running water at the base of the hill. A foundation for the 

 meridian-circle piers was obtained by levelling one of the strata in situ, and to this their bases 

 were secured with hydraulic cement. Composed of three blocks, each pier, formed an obelisk 

 eight fec-t high, two feet square at bottom, and one foot at top. Shortly after mounting the 

 instrument, its eastern pivot was found to be rising slowly though constantly, and at last an 

 error accumulated that was inconveniently great. At first this was attributed to unequal 

 shrinking of the cement between the three joints of each pier, and to the plaster used in securing 

 the several adjuncts ; but time brought no change, and within the following ten months the 

 support under that- pivot was lowered 49". 3, or an average of very nearly 5" per month. Then 

 followed the succession of earthquakes in April, during which changes of adjustment were fre- 

 quent, though the records do not tell to what extent the screws were altered. However, it is 

 very sure that the eastern extremity of the axis was never elevated by the screw. During most 

 of the winter, and until August, the axis remained quite steady. In the latter month a motion 

 equal to 5" took place in the opposite direction ; but from the commencement of spring, and 

 until the close of the following autumn, the same uplifting of the east pier ensued, so uniform 

 in its monthly amount that the change of error from this cause could be calculated within a 

 second or two. In seven months the support was, of necessity, lowered 45" more, making 1' 34" 

 in twenty-two months ; and then, during the remainder of our sojourn, as throughout the pre- 

 ceding winter, the axis fluctuated about a horizontal line, with a tendency upward of its western 

 pivot. 



The two piers are from the same quarry of red porphyry, similar in form and dimensions, 

 based on the same rock ; in fact there is no reason apparent why one should change more than 

 the other. How is this elevation of the eastern pier to be accounted for? Do the Andes still 

 rise, as might a hinge, of which the coast line formed the axis, or is it only that Santa Lucia is 

 tilting over to the westward ? And if so, why do the rains of winter interrupt the progressive 

 elevation ? No satisfactory responses to these questions have yet offered themselves, and the 

 facts are presented, as perhaps connected with geology and earthquakes. I cannot believe that 

 any elevation so rapid as these measures indicate is going on ; for the length of the axis of the 

 meridian-circle being forty inches, its eastern pivot was moved nearly two hundredths (.0182) 

 of an inch (!' 34") in twenty-two months ; or, on the supposition that the basin of Santiago 

 changed at a uniform angle, the base of the Andes rose sixty feet more than the Cordilleras to 

 the west an amount too great to have escaped detection, even by the eye alone. Moreover, 

 the westerly inclination apparently continues as it was thirty years ago, although it is well 

 known that nearly half an inch of silt is annually deposited in artificial irrigation of the culti- 

 vated estates, and that the drainage from east to west is very great during the excessive rains 

 of winter. One might infer that the two sides of the basin would have approximated to a level 

 from these causes, even unaided by washings from the Western Cordilleras. 



Other effects yet more disastrous than the loss of edifices and property have been attributed to 

 earthquakes by more that one writer. Public health is alleged to be affected ; whole districts, 

 previously fruitful, have become hopelessly sterile, and certain classes of trees wither and die of 

 the poison which is imparted to the soil during the convulsion. With regard^to the first of 

 these, too little is known of the normal sanitary conditions of the several countries prior to great 

 earthquakes to warrant inference that subsequent endemics were due to them. It is certain that 

 there were more than the usual number of fatal diseases after the earthquake of 1822 ; and some 

 of the physicians of Santiago* consider that the virulence of several epidemics as dysentery, 

 erysipelas, and aneurism has increased since that epoch. That much sickness should imme- 

 diately follow, is readily explicable from the influence of exposure whilst half clad. Terror, and 



* Analea de la Univereidad, 1849 and 1850. 



