and the equator (the zero for latitude) was the Survey’s sheet-anchor. Madras was in effect the Indian Greenwich. And when, as happened, some infinitesimal adjustmentwas made to the coordinates for the Madras Observatory, Lambton’s whole web of triangles had to be realigned.
Other such adjustments would necessitate further mind-boggling recalculations. A later writer estimated that the trigonometrical surveying of India involved 9,230 unknowns and produced ‘unwieldy equations exceeding anything of the kind ever attempted’. Trial and error, leading to constant refinement, played no small part in the geodesist’s science. His situation was like that of a farmer trying to sow his drill evenly with an uncertain number of seeds. When the seeds ran out before he reached the end of the drill, he must needs go back and respace them; and likewise if he came to the end with seeds to spare. Repeating and reviewing past work was as important as prosecuting new work.
For example, the length of a degree of longitude as calculated from that short arc carried south from Madras in 1802 was soon revised when the Great Arc produced a more refined value. That in turn meant that the earliest triangles based on the Madras measurement had also to be revised. As the Arc got longer, other assumptions about the curvature of the earth were reassessed, and these in turn meant more recalculation. Lambton had at first accepted Sir Isaac Newton’s figure of 1/230 for the compression of the earth’s spheroid at the poles. However this ‘constant’ proved anything but. It was revised down to 1/304 in 1812 and by Lambton himself to 1/310 when in 1818 his Great Arc had embraced nearly ten degrees of latitude. Everest in turn would come up with his own constants; and every new constant meant recalculating all previous work.
Further complications arose from attempts to refine standards of length. Lambton’s anxieties over the elasticity of Dinwiddie’s chain increased with every base-line measurement. When the chain unaccountably stopped expanding as measured against the one held in reserve, he became suspicious about the reliability of the latter as a standard. As once before,a hundred-foot brick wall was constructed, tents erected over its entire length, and its surface levelled and polished ‘so as to resemble a sheet of glass’. Both chains were then stretched along it, their relative values being assessed by micrometer against a standard bar and then marked against pre-set brass studs, mounted in lead, and set in concrete.
Matters were not assisted when in 1821 a parliamentary committee in England laid down a new standard of length. Lambton had long urged the adoption of such a standard, although he would much have preferred that based on the decimal metre and its derivatives as already calculated by the French. The British ignored this advice. In London Henry Kater reduced the new standard to the scale used by Cary in calibrating the dial of Lambton’s Great Theodolite. Lambton had then again to go right through all his measured angles and readjust them.
It was hardly surprising that he had little time for fieldwork. As he patiently explained to the Calcutta authorities, he could not simultaneously continue the surveying and process its results. The calculations involved were so complex that they could be entrusted to no one else. Even producing a fair copy of one of his reports took five months and, because of its highly technical nature, it could not be delegated. Instead he must delegate the fieldwork. If the government were unhappy with this arrangement, they must supply him with a senior assistant; and while they were about it, he also badly needed a doctor and a geologist.
The doctor was required to minister to Lambton’s survey parties, who were continually having to quit the field because of fever, while the geologist was needed to sort out his problems with the plumb-, or plummet-, line. Although the Great Arc was providing
Other such adjustments would necessitate further mind-boggling recalculations. A later writer estimated that the trigonometrical surveying of India involved 9,230 unknowns and produced ‘unwieldy equations exceeding anything of the kind ever attempted’. Trial and error, leading to constant refinement, played no small part in the geodesist’s science. His situation was like that of a farmer trying to sow his drill evenly with an uncertain number of seeds. When the seeds ran out before he reached the end of the drill, he must needs go back and respace them; and likewise if he came to the end with seeds to spare. Repeating and reviewing past work was as important as prosecuting new work.
For example, the length of a degree of longitude as calculated from that short arc carried south from Madras in 1802 was soon revised when the Great Arc produced a more refined value. That in turn meant that the earliest triangles based on the Madras measurement had also to be revised. As the Arc got longer, other assumptions about the curvature of the earth were reassessed, and these in turn meant more recalculation. Lambton had at first accepted Sir Isaac Newton’s figure of 1/230 for the compression of the earth’s spheroid at the poles. However this ‘constant’ proved anything but. It was revised down to 1/304 in 1812 and by Lambton himself to 1/310 when in 1818 his Great Arc had embraced nearly ten degrees of latitude. Everest in turn would come up with his own constants; and every new constant meant recalculating all previous work.
Further complications arose from attempts to refine standards of length. Lambton’s anxieties over the elasticity of Dinwiddie’s chain increased with every base-line measurement. When the chain unaccountably stopped expanding as measured against the one held in reserve, he became suspicious about the reliability of the latter as a standard. As once before,a hundred-foot brick wall was constructed, tents erected over its entire length, and its surface levelled and polished ‘so as to resemble a sheet of glass’. Both chains were then stretched along it, their relative values being assessed by micrometer against a standard bar and then marked against pre-set brass studs, mounted in lead, and set in concrete.
Matters were not assisted when in 1821 a parliamentary committee in England laid down a new standard of length. Lambton had long urged the adoption of such a standard, although he would much have preferred that based on the decimal metre and its derivatives as already calculated by the French. The British ignored this advice. In London Henry Kater reduced the new standard to the scale used by Cary in calibrating the dial of Lambton’s Great Theodolite. Lambton had then again to go right through all his measured angles and readjust them.
It was hardly surprising that he had little time for fieldwork. As he patiently explained to the Calcutta authorities, he could not simultaneously continue the surveying and process its results. The calculations involved were so complex that they could be entrusted to no one else. Even producing a fair copy of one of his reports took five months and, because of its highly technical nature, it could not be delegated. Instead he must delegate the fieldwork. If the government were unhappy with this arrangement, they must supply him with a senior assistant; and while they were about it, he also badly needed a doctor and a geologist.
The doctor was required to minister to Lambton’s survey parties, who were continually having to quit the field because of fever, while the geologist was needed to sort out his problems with the plumb-, or plummet-, line. Although the Great Arc was providing
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