THE CLIMATE. g7 



aim, the temperature of water may fall 2 or 3 below the freezing-point before ice 



forms."* 



The formation ( .i' masses of ice in the atmosphere belongs rather to electrical phenomena, 

 ami would nmrc properly have followed notice of the thunderstorms of the Andes, so common in 

 .summer. There was only one during the three years, viz: on the 13th January, 1852. It 

 commenced suddenly about 4 p. M., after a day moderately overcast by masses of cumuli and 

 a l"\v temperature, (68 at 3 p. M.) and was unaccompanied by lightning. The stones were 

 truncated cones and pyramids, with spherical bases, as though they had formed portions of 

 spheres perhaps an inch in diameter. Their bases were of a milky yet translucent ice, whilst 

 the upper halves were softer, whiter, and more opaque. The storm lasted about ten minutes, 

 though the sky remained clouded over until after 7 p. M., and occasional drops of rain fell all 

 the afternoon. Two miles west of the observatory there was a violent squall of wind, but no 

 hail ; and on the distant summits of the Andes a large body of snow, or hail, was deposited. 

 At night the thermometer fell below 50, the barometer remaining nearly 0.15 inch above its 

 mean height a very great variation from its normal elevation, in a country where the fluctua- 

 tions are so small. 



Ordinarily, the air is calm from about sunrise until between 9 and 10 o'clock A. M., at which 

 time a wind commences from the S.W. This increases in strength till 2 or 3 p. M., and then 

 moderates as gradually to sunset, when it is again calm. Its violence on the plain was rarely 

 more than what, in nautical parlance, is called " a fresh breeze;" but on the elevated summits 

 of the Andes, over which it also extends, it is usually excessive. Lieut. MacRae wrote me that 

 it was so strong when he arrived at the pass of the Cumbre, between Santiago and Mendoza, 

 that, as early as 10 A. M. it almost overturned both mule and rider; and arrieros declare they 

 have seen small stones blown away by it. Deep ravines debouching on the plain near Santiago, 

 and many hills near it, cause so many deflections as to render it impossible to determine the 

 true direction of this wind by estimation ; nor will it be practicable to do so, except by placing 

 a register anemometer half-way across the plain. Our guides were, the direction that smoke 

 was moved, or, failing this, the plane in which some of the lofty and pliant poplars were inclined. 

 From these we found that the current varied in its direction from W.S.W. to S.S.W., and 

 when strongest was most generally from S.W. These winds are attended with a clear atmo- 

 sphere, and the only clouds to be seen are formed within the valleys of the rivers, at elevations 

 of 5,000 to 10,000 feet above the plain, and which continue ascending until they rest in heavy 

 cumulous masses over the elevated range. Vapor is rarely condensed immediately over the 

 valley during the day, but a line not unfrequently collects at night half-way up the near chain, 

 and remains there until dispelled by the heat of the day. With night the entire mass above 

 the Andes disperses, though not until after a display of lambent sheets of lightning, sometimes 

 continuing beyond midnight. Whenever similar corruscations were seen over the central range 

 to the N.W., as was the case on two or three occasions, they were invariably followed by rain. 



After sunset " el ten-al," or, as it is called in the south, " d pudche," a land breeze, com- 

 mences. This, first perceptible on the coast, recedes slowly towards the Andes, where it is 

 scarcely felt until near morning, thus proving itself a true wind of aspiration. Its apparent 

 direction is modified at Santiago by causes analogous to those influencing the "travesia," as 

 the day wind is named ; and we find it one night from N.E. ; the next, perhaps, or even at a 

 subsequent hour of the same night, from S.E. It is never more than "a light breeze," and 

 ceases entirely throughout its range by sunrise. 



Late in the season a sort of dry fog, resembling thin smoke, deprives the atmosphere by day 

 of something of its transparency, though the nights are all that the astronomical observer can 

 desire. Then the Andes, whose crests are not less than 18 miles distant in an air- line, look 

 almost within stone-throw, and the stars rise over them with a steadiness and brilliancy known 



* Anales do 1& Univenidad do Chile, Junio, 1851. 



