'History of the Indian Navy. (1613-1863).' [‎402] (421/622)

402
HISTORY OF THE INDIAN NAYY.
speed, as tested by the standards, were liable from any acci
dental deviation frem the vessel's straight course, these ob
servations were taken very frequently, and their results were
very satisfactory, as the vessels steered as steadily as could be
desired, the flat being towed alongside the steamer. The speed
of the vessels over the ground, the progress being against the
stream, averaged eighty or ninety yards per minute, in excep
tional cases ranging so low as thirty-five to forty, and so high as
one hundred and sixty. The rate through the water was found in
the ordinary way. A Burmese was at hand to give information
as to the names of the villages, &c., and as every point could not
be named (nor, if so, would it have been convenient to use
their names), each point or other object was denoted by the
degree of the prismatic compass by which it first came under
observation. The vessels were always moored to the bank
shortly after sunset. Then came observations of stars, with
the artificial horizon for latitude and longitude; and as our
stay at the principal places en route generally extended to a
day, very frequent opportunities were found for ascertaining the
rates of the chronometers. Chronometer measurements were
thus obtained under circumstances peculiarly favourable, and
they were again checked on the return passage of the vessels.
This survey does not pretend to mathematical precision; it is
merely a sketch-survey, rapidly taken under peculiar circum
stances. Perhaps the astronomical observations are its most
valuable results; nevertheless, the sketch itself will be found
to possess such a degree of accuracy as can ordinarily be ob
tained when the opportunities for surveying are no greater
than those afforded by the passage up an almost unknown
river for the first time in a steam vessel. At Amarapoora a
trigonometrical survey of the water-approaches to the capital
was obtained, as also a section of the river at a favourable
point, and the discharge of water at the prevailing season."
Between the years 1856-62, Lieutenant Heathcote was
engaged upon the surveys of the Bay of Bengal. In the
former year he made a survey of the western entrance of the
Hooghly from Kaokali to the Pilot Station at the Sand Heads.
"It was undertaken," says Markham, "because the Gaspar
Channel, that commonly used, was becoming dangerous, owing
to accumulations of sand, and threatening to obstruct the
traffic to Calcutta. This survey, which required very great
exactness, was performed in the surveying vessels, 'Krishna'
and 6 Spy,' and the chart was drawn on a large scale, showing
the depth of water to feet. It was accompanied by a report
upon all the channels of the Hooghly, comparing their present
form with that which they showed upon the last surveys, and
showing the amount of accumulation that had taken place.
The work was connected with the stations of the Great Trigo-