longitudinal
arc at the same time and immediately sought out a likely
site.
As soon as the catch-up administrative work that had
amassed in his absence was on the way to being cleared
he set out to plan this new baseline. It took 45 days
and nearly 100 personnel to complete the nearly 34 000
feet. The value calculated through the 671 miles from
Sironj agreed with the measured value to 7 ft 11 inches.
The base itself was considered to be good to little
more than 1 inch.
In late 1832 Everest moved his headquarters from Calcutta
to Dehra Dun where it remains to this day. As will be
seen later, however, he also established a personal
estate in the hills above Mussoorie. By then he was
thinking of a control baseline on the meridian arc and
seeking a suitable site near Dehra Dun. However before
being able to do that it was necessary to triangulate
across the flat Doab region from Agra northwards to
Delhi and then on towards Dehra Dun. It was so flat
that in one stretch of 160 miles there was only a rise
of some 268 feet. It was 1835 when it became possible
to measure the Dehra base and complete the meridian
chain from Sironj. Measured twice, this base was nearly
39 200 feet long and the repeated measure agreed to
2.4 inches with the first. Thus with the Calcutta and
Dehra baselines proved the worth of the compensating
bars.
During extended periods Everest was again laid low with
illness but struggled onwards both on the Arc and with
minor series. He had new instrumentation in the form
of two astronomical circles, but these caused some problems.
He had a workshop at his Estate in the hills and there
spent much time supervising changes to these instruments
until he was happy with their operation. |