On the 21st of August, we rose early, excited alike by the novelties of the neighbourhood, and by the occurrence of another term-day. Our interpreter and his men had done their work famously in the preceding week, having erected altogether something like sixty yards of wall, four feet thick and six feet high; and so arranged, as to form a telescope enclosure in the centre, with cells or small rooms round about. One of these, intended subsequently for optical experiments, was soon furnished with half a roof over its southern end; and there we established the meteorological instruments.

The barometer was at 20·5 inches; the thermometer at 6 a.m., was 49°; and at noon, its maximum, was 65°. The air was thus found very sensibly cooler here, than on Guajara; while the dryness was rather less, the depression of the dew point varying from 18° at night, to 41° in the middle of the day. The power of radiation, however, appeared to be increased, and the inclination therefore, in the temperature, to mount up to a maximum with noon, became its marked feature.

The earlier part of the solar course, or from the eastern horizon upwards, could be well commanded at Alta Vista; but at 3h. 45m. p.m., the sun was lost behind the western lava ridges of the Peak; while other descending streams, on the immediate N. and S. of our station, cut off the lower part of the sky in those directions also.