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of the angles measured with the great theodolites range from 
+2 to +5. The probable errors of the trigonometrically 
deduced ratios of the sides of the triangles are functions of 
those of the angles and of the geometric conditions of the 
triangulation. When the number of triangles is small the pro- 
bable errors of the trigonometrical ratios are less than those 
of the ratios of the base lines, but in certain representative 
chains of triangles, averaging 575 miles in length and com- 
posed of a large number of triangles, the probable errors of 
the trigonometrical ratios of the base lines at their extremities 
are about three times those of the linear ratios. Thus the 
trigonometrical and the linear operations are fairly on a par 
with each other as regards accuracy. 
Col. Walker then proceeded to give an account of the work 
which has been completed up to the present time, and shewed 
what remains to be done to finish the programme of operations, 
He pointed out that the present desideratum in geodesy is 
not so much a better determination of the mean figure of the 
earth, as of the variable figure at different parts of the earth’s 
surface; and he stated that the operations of the Indian survey 
will, when supplemented by appropriate astronomical operations 
and differential determinations of longitude by the electric 
telegraph, furnish a number of meridional arcs and arcs of 
parallel which will be of great geodetic value. 
The paper closed with an exposition of the methods which 
have been introduced by the author for the final reduction of 
the whole of the triangulation, so as to render all the parts 
consistent and harmonious. 
Mr Exits asked if there were any signs of the earth’s 
expansion or contraction during the measuring of a base line. 
Col. WALKER said it could not be detected while an opera- 
tion was going on. However, after an earthquake in Eastern 
Cachar the officer in charge asserted that the distance of some 
of the stations had been altered, but it was not certain whether. 
