Oman in
the east, the summer heat is never excessive, and the winters are,
comparatively speaking, cold.

In the northern desert the temperature is subject to extreme
variations. Nolde states that on the 1st of February 1893 in the
desert north of Hail the thermometer fell from 78 deg. a little before
sunset to 18 deg. a quarter of an hour after. The midday temperatures
recorded by Huber at Hail during January and the first half of
February average about 65 deg. F., and water froze on several nights;
at Medina the winters are cold and night frosts of frequent
occurrence, and these conditions prevail over all the western part of
the Nejd plateau. In the east where the elevation is lower the climate
is warmer. In the elevated highland district which extends from Taif
to within 50 m. of Aden, the summer heat is tempered by the monsoon
winds, and the seasonal variation of temperature is less marked. From
observations made at Sana by Manzoni, Deflers and Glaser, the mean
temperature for the year of that city at an altitude of 7300 ft. and
in 15 deg. 22' N. appears to be 60 deg. F.; for July the mean maximum
was 77 deg., mean minimum 54 deg.; for January the figures were 62
deg.and 40 deg. respectively, the lowest recorded temperature in 1878
was 26.6 deg. on the 26th of January. At Aden at the sea-level the
mean temperature for the year is 83 deg.; the highest observed
temperature in 1904 was 97.3 deg., the lowest 67.4 deg.

The rainfall throughout northern and central Arabia is chiefly in the
winter months between October and April, and is scanty and irregular.
Doughty states that in 1876 rain to wet the ground had not fallen for
three years at Medain Salih; in that year showers fell on the 29th of
December and on two days in January and again in March. After a very
hot summer the bright weather changed to clouded skies on the 2nd of
October, rain fell tempestuously the same evening, and there were
showery days and nights till the 14th. The autumn rains fell that year
abundantly in the Nafud towards Jauf, but very little in the basin of
the W. Hamd (on the western slope). Doughty adds that the Nejd
highlands between Kasim and Mecca are watered yearly by seasonable
rains, which at Taif are expected about the end of August and last
commonly from four to six weeks. This appears to be about the northern
limit reached by the south-west monsoon, which from