— 95 — 
and which may be reading 17 cubits while Cairo may be recording 25 
cubits. The Cairo gauges in winter and summer are no records of 
discharge as the afflux from the Barrage affects them. To find the 
discharge at Cairo during these months, I have added those of tho 
Rosetta and Damietta branches and the Delta canals upstream of the 
Barrage. When the Nile falls below mean low water level, the gauges 
are recorded as minus quantities. 
Discharge sites having been chosen for the Assuan, Assiout and 
Cairo gauges on the Nile, a continuous series of surface velocity obser- 
vations, cross sections and slope measurements were made during 1892 
and 1893 and the resulting discharges recorded. Curves of discharge 
have been drawn and referred to the gauges of twenty years and mo- 
dified until finally a curve has been found which will suit any year 
whether it is a maximum or a minimum. In connection with this 
subject, it must be remembered that the Nile bed is raised by silt 
during low floods and scoured out during high floods and that conse- 
quently August and September discharges vary considerably at times 
from October and November discharges for the same gauge. In ad- 
dition to this, it must also be borne in mind that the slope of water 
surface and that consequently the discharge of a flood during the rise 
is far greater than during the fall for the same gauge reading. Indeed 
the Nile often discharges more when it is 30 centimetres below its 
maximum and rising fast than when it has reached its maximum and 
begun to fall. It is owing to this fact that we often see the discre- 
pancy of the Assuan gauge reaching its maximum a day before Haifa 
which is 350 kilometres higher up the river. The discharge depends 
on gauge and slope, and the gauge only records one element. Keeping 
these facts in my mind, I saw that it was of no use recording the 
gauges to two places of decimals and covering paper with useless 
figures, and consequently I have chosen the higher unit for a rising 
gauge and the lower for a falling gauge when I have been dealing with 
discharges. 
Flood discharges have been taken of all the canals in Upper Egypt 
through 1892 and 1893 and have been recorded in Tables 48 and 49 of 
Appendix K. From these tables, Table 47 has been compiled which 
gives rough approximate discharges of the canals corresponding to the 
Assuan gauges in the first half of the flood. 
To obtain information about the trough of the Nile, the area exposed 
to evaporation and the area of absorption, a longitudinal section of the 
