1895.] 
C. F. Oldham —Topography of the Arabian Sea. 
3 
although in different years—the thermometers used being the Miller- 
Casella pattern, constructed by Cavy of London ; and the observations 
being corrected for the errors supplied from Kew Observatory—shew 
that the waters of the eastern part of the Laccadives, in depths over six 
hundred fathoms, are considerably warmer than the waters towards 
the Hindustan coast, and than those to the westward of the Laccadives. 
On the plateau a temperature of 41° F. is reached at a depth of 905 
fathoms, while the same temperature is met with at 790 fathoms on the 
thousand fathom line near the coast. 
The bottom temperatures on the western side appear somewhat 
erratic, but with one exception they all tend to shew a higher, tempera¬ 
ture over the plateau than on either side. The surface temperatures 
vary from 77° F. to 83° F., the highest temperature being in the neigh¬ 
bourhood of the reefs. 
The isothermal lines vary in deptb to 400 fathoms, after which 
they are even to 600 fathoms, from 700 until the bottom is reached they 
dip downward in the centre owing to the warmer waters over the 
Laccadives. 
A curve shewing the mean temperature at different depths 
from the surface to 1,300 fathoms, is shewn in black at Plate 
II. From the surface to 100 fathoms the curve depends on one 
series of observations taken every 25 fathoms ; from 100 to 400 fathoms, 
it depends on twelve observations at varying depths, and from 400 to 
1,300 fathoms, the curve is the mean result of fifty-six observations : all 
these observations were taken in the months of October, November, or 
April, at the change of the monsoons. The curve shewn in red on the 
same figure is taken from Commander Carpenter’s paper on the mean 
temperature of the deep waters of the Bay of Bengal. It is derived 
from observations taken during the fine season—November to May. 
The Arabian Sea curve to 100 fathoms depends on so few observa¬ 
tions that it is not desirable, up to this depth, to make any comparison 
with the Bay of Bengal curve. Beyond 100 fathoms, where the 
observations are numerous, it will be noted that there is a difference 
of about one to two degrees ; the Arabian Sea on the west coast of 
Hindustan in October, November, and April, being that amount warmer 
than the Bay of Bengal. At a depth of 1,300 fathoms the two curves 
coincide. 
Sections of some of the Laccadive islands and reefs—the direction 
of the sections taken being generally at right angles to the length 
of the islands—show that the under-water slopes vary from 10 to 27 
degrees, and that the slopes of the lagoon islands are rather steeper than 
that of reefs, at Betra Far and Feremul Far. At Kardamat the bottom 
