TRANSACTIONS OF SECTION E. 1131 
melting snows, is about 14°. At a great depth the difference is greater, a circum- 
_stance which is turned to practical use at Attak. 
The fall of these rivers beiag greatest in the hill portion of their course, and 
decreasing as they come down through the plains, the vertical section of their 
course is a curve terminating in a nearly horizontal line at the sea. From Attak 
to Kalabagh the fall of the Indus is 50 inches per mile, from Kalabagh to Mittan 
Kote 12, and from Mittan Kote to the sea 6, the end part being less. The result is 
a constantly increasing tendency to deposit silt and raise the bed, and by overflow 
to raise the banks. For a great part of its course the Indus flows in a channel 
slightly above the level of the land on either side. 
The local rainfall of the country through which these rivers flow in the Punjab 
diminishes gradually in quantity from their first entrance on the plains to the place of 
their junction above Mittan Kote. The Chinab issues from the hills in a region of 
51 inches annual rain, the Indus and the Jhelam 36, the Ravi and the Bids 53, 
the Satlaj 26; and their common confluence is in a tract of country which has no 
more than 6 inches rain in the year. The great floods which they all bring down 
in the rainy season are of course chiefly due to the more copious rainfall in the 
hill country from which they come. To meet in some measure the local want of 
water thus increasing southward, the rivers are made to give off part of their 
supplies in canals, which fill as the river rises. Canals, carrying water permanently 
throughout the year, are drawn off from some of the-rivers in the upper part of 
their course near the foot of the hills, and are carried along high land for the 
supply, all the way, of the country right and left. So great areas of land are 
protected against the possible eflects of their scanty and precarious rainfall. 
Where these canals and their branches flow, the level of water in the wells is 
raised, and thus more advantage can be taken of the great sheets of water at 
varying depths below the surface. In the country through which run the dry 
channels of the Saraswati, Gaggar, Markanda, &c., the depth of the wells is very 
great, but the rainfall, though small (about 18 inches), is much greater than in the 
country to the west, at the tail of the Punjab rivers. 
Besides the windings and changes of channels for short distances, with general 
maintenance of the same line, there are deviations ona larger scale, rivers forsaking 
old lines and taking an entirely new course. One well-known instance of this 
among the Punjab rivers is that of the Ravi, of which a deserted channel is trace- 
able for a long distance in the Lahore and Montgomery districts. 
The Punjab rivers are of different colours, depending on the soil through which 
they have passed and the tributaries they have received. The different colours of 
two rivers is often observable for a long distance below their confluence. The 
Indus below Attak is dull blue; its tributaries in this part of its course are red, 
except the Harro, which is light in colour and comparatively clear. The Ghana 
(Satlaj) is light but not clear where it is joined by the red Chinab, and they run 
on for a long way not mixed. 
The united rivers which join the Indus are of less volume and velocity than 
its single stream. The width of the Panjnad (the combined five) is more than 
twice that of the Indus, but its depth is smaller and the rate of its current less than 
one-half. In the low season the discharge of the Indus is 92,000 cubic feet per 
second, and of the Panjnad 69,000—in all 161,000. The flood discharge in the 
month of August below the junction has been estimated at 446,000 cubic feet. 
Such rivers are great powers, very valuable, and difficult to deal with. By 
watching their characters, and obeying while controlling the action of nature, we 
can do much to make them subservient to our purposes, and in some measure 
to illustrate man’s influence on the physical as well as political geography of a 
country. 
8. On a Clinometer to use with a Plane-Table. By Major Hut. 
9. On a supposed Periodicity of the Cyclones of the Indian Ocean, south of 
the Equator. By Cuartes Metprum, F.2.S. —See Section A, p. 925. 
