1116 nerort—1885. 
rarely raised to a greater height than 30 feet, or just sufficient to overtop the 
curvature, and all trees and other obstacles were cleared away on the lines between 
‘them ; this was found the most expeditious and economical process. The stations 
were very substantial, with a central masonry pillar, for the support of a great 
theodolite, which was isolated from the surrounding platform for the support of 
the observer. The lofty Russian scaffoldings only sufficed for small theodolites, and 
they were so liable to shake and vibration that the theodolites had to be fitted with 
‘two telescopes to be pointed simultaneously by two observers at the pair of stations, 
the angle between which was being measured. 
All the modern geodetic data of the Indian survey that were available up to 
the year 1880 were utilised by Colonel A. R. Clarke, C.B., of the Ordnance Survey, 
‘in the last of the very valuable investigations of the Figure of the Earth which he 
has undertaken from time to time. It will be obvious that new data tend to modify 
in some degree the conclusions derived from previous data, for the figure of so large 
-a globe as our earth is not to be exactly determined from measurements carried 
over a few narrow belts of its supertficies. Thus thirty years ago it was inferred 
that the equator was sensibly elliptic—and not circular, as had been generally 
assumed—with its major axis in longitude 15° 34’ east of Greenwich ; but later in- 
vestigations indicate a far smaller ellipticity, and place the major axis in west lon- 
gitude 8° 15’. More significant evidence of the influence of new facts of observation 
in modifying previous conclusions is furnished by the French national standard of 
length, the métre, which was fixed at the ten-millionth part of the length of the 
arth’s meridional quadrant, as deduced from the best geodetic data available up to 
the end of the last century; but it is now found to be nearly =.th part less than 
the magnitude which it is supposed to represent, the difference being about a hun- 
dred times greater than what would now be considered an allowable error in an 
important national standard of measure, 
The Indian survey has also made valuable contributions to geodesy and geo- 
gnosy in an elaborate series of pendulum observations for determining variations of 
gravity, which throws light both on the grand variation from the poles to the 
equator that governs the ellipticity, and on the local and irregular variations depend- 
ing on the constitution of the interior of the earth’s crust. “They were commenced 
in 1865 by Captain J. P. Basevi, on the recommendation of General Sabine and 
the Council of the Royal Society, with two pendulums, one of which the General 
had swung in his notable operations which extend from a little below the equator 
to within 10° of the pole. Captain Basevi had nearly completed the operations in 
India, and had taken swings at a number of the stations of the Great Are and at 
various other pots near mountain ranges and coast lines, when he died of exposure 
in 1871 at a station on the high table lands of the Himalayas, while investigating 
the force of gravity under mountain ranges. Major Heaviside swung the pendulums 
at the remaining Indian stations, then at Aden and Ismailia on the way back to 
England, and finally at the base station, the Kew Observatory. Afterwards 
they and a third pendulum were swung at Kew and Greenwich by Lieutenant- 
Oolonel Herschel, who took all three to America, swung them at Washington, 
and then handed them over to officers of the United States Coast Survey, by whom 
they have been swung at San Francisco, Auckland, Sydney, Singapore, and in 
Japan. 
"The pendulum operations in India have been successful in removing from the 
geodetic operations the reproach which had latterly been cast on them, that their 
‘value has become much diminished since the discovery that the attraction of the 
Himalayan mountains is so much greater than had previously been suspected, that 
it may have materially deflected the plumb-line at a large number of the astronomi- 
eal stations of the Great Arc, and injuriously influenced the observations. Everest 
considered the effects of the Himalayan attraction to be immaterial at any distance 
exceeding sixty miles from the foot of the mountains; but in his days the full 
extent and elevation of the mountain masses was unknown, and their magnitude 
was greatly underestimated. Afterwards, when the magnitude became better 
known, Archdeacon Pratt of Calcutta, a mathematician of great eminence, calculated 
that they would materially attract the plumb-line at points many hundred miles 
