"نجد الجنوبية: رحلة إلى الخرج والأفلاج والسليل ووادي الدواسر في سنة ١٩١٨." [ظ‎‎٤‎٤] (١٠٠/٩٣)

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plain districts up to, and then westward along, the Birk. The
" hot " zone would thus include Aridh, Kharj, Alfara, and the
plain district of the Aflaj, while the hill district of the latter,
the Tuwaiq plateau south of it, Sulaiyyil and the wadi would
fall into the " cool " zone. During the period from June 7 and
June 15, spent in traversing the three most southerly section
of Tuwaiq, the prevailing wind was from the north and of
varying steadiness and intensity, a normal daily record being
somewhat as follows :—
From 4 a.m. to 7 a.m.—no wind.
From 7 a.m. to noon—light north wind gradually increasing
in intensity.
From noon to 4 p.m.—north wind strong and gusty.
From 4 p.m. to 6 p.m.—moderate to light north wind.
From 7 p.m. to 4 a.m.—no wind.
The average maximum and minimum temperatures for this
peiiod were 102'2 and 65*96 respectively, the lowest maximum
and highest minimum recorded were respectively 95-90 and
73-40 (both curiously enough on the same day, namely June 12) ;
while the lowest minimum and highest maximum touched were'
lespectively 59-52 and 105*8 (again both on the same day,
namely, June 10). The average temperature at 8 p.m. was
85-1 and between 11 p.m. and midnight 76. It will be seen
from this record that the climatic conditions experienced during
the second fortnight of June were about as pleasant as one
could reasonably expect at such a season between latitudes
21 and 23^° in a country accounted tropical.
These conditions, however, underwent a distinct change
for the worse in the second period extending from June 19 to
June 23, during which, it should be observed, we were very near
to, or actually outside, the eastern boundary of Tuwaiq. The
wind now became very uncertain with a prevailing tendency to
come from the south-west or south. The lowest temperature
recorded was 65-30 on June 19, the highest 112-10 on the
following day at the mouth of the Fara, the average maximum
and minimum were 110-41 and 71-10 respectively; while at
8 p.m. and midnight the average readings were respectively
86 and 80-3. Even such a record compares very favourably
with what one is accustomed to at this season in Mesopotamia
and India.