1124 REPORT—1885. 
error or systematic accumulation of minute constant error; yet a source of minute 
but cumulative error remained which, coming from an external quarter, was not 
guarded against by alternating the direction of operation or by any of the ex- 
pedients adopted for eliminating inherent cumulative errors. It lay in the admitted 
tendency there is, when levelling an instrument, to unduly depress the telescope in 
the direction of the light which illuminates the spirit-level of the instrument, thus 
making all objects viewed through the telescope, when pointed in that direction, 
appear too high. The sun was the invariable source of illumination, and it was 
always to the south of the observer, and therefore the southern ends of the lines 
of levels would have a tendency to be brought out too high. This illumination 
error is a maximum on the meridian and vanishes on the prime vertical ; however 
great its magnitude, it re-enters and is non-apparent in a circuit of levels; it would 
only be apparent on lines starting and closing at different points on the mean sea, 
which gives an independent check on the accuracy of the line of levels. It isa 
vera causa of error such as has actually been met with; but there is now some 
reason to doubt whether it really was the cause, for the two lines next measured 
from sea to sea brought the northern ends out highest, and a third line recently 
completed shows no appreciable difference between the north and south ends. The 
later results may, however, be due to the observers having been more careful to 
guard agairst illumination error. In seven lines out of the eight the discrepancies 
are small, not exceeding two inches in 100 miles of line; but there is one large 
discrepancy of 4? inches per 100 miles, accumulating to 8 ft., on the line between 
Bombay and Madras. The two weakest sections of this line have been re-levelled, 
but in each instance with results which were identical with those first obtained. If 
the observations are errorless in themselves, error must have been introduced by 
the local attractions encountered on the line which crosses the western ghats and 
the elevated plateau lying between Bombay and Madras. These attractions would 
obviously influence the levels of the contiguous instruments in a greater degree 
than the distant waters of the ocean. 
3. Notes on the Physiography of Southern India. 
By Colonel B. R. Branritt, 
The part of India to which these notes are confined lies to the south of latitude 
15°, and mostly in the Madras Presidency. Its principal characteristics are great 
diversity of feature and mildness of climate, which, though tropical, is almost 
insular, and entirely subject to the effects of the south-west and the north-east 
monsoons. It is a region of mountains and hills, elevated table-lands and low-lying 
flats, fertile plains and barren wastes, flooding rivers with beautiful waterfalls and 
innumerable artificial lakes, tropical forest, endless groves, and jungly wilderness. 
Southern India is an interesting field of observation for the naturalist, and par- 
ticularly for the physiographer, on account of the elements of change in active 
operation :—firstly, the decomposing and disintegrating power of the sun’s rays, 
vertical twice every year; secondly, the long-continued violent winds that scour 
the surface and transport immense volumes of matter to great distances in the air, 
and, by means of the ocean waves, along the shore; thirdly, the torrents of rain 
that denude the hill surfaces and score the slopes with deep channels, depositing 
the spoil on the flooded flats, the growing deltas, and the shoaling shore. 
Many other elements of change are at work, and the earthquake alone seems 
wanting. These agencies seem fully adequate to the task of converting a vast 
plateau of igneous matter, overlying a granitic base, into the subdued and diversi- 
tied area we now behold. 
For the purpose of these notes the author divides Southern India into three 
tracts. First, the mountainous region of the Ghats, including the higher table- 
lands and the great upland plains of Maistir contained between the Western and 
Eastern Ghats. Second, the lowlands of the Malabar coast: all that narrow tract 
of moist sea-board between the foot of the Western Ghats and the Arabian Sea. 
* Printed in the Proceedings of the Royal Geographical Socrety for November, 1885. 
