'History of the Indian Navy. (1613-1863).' [‎401] (420/622)

HISTORY OF THE INDIAN NAVY.
401
f the " Journal of the Royal United Service Institution,"* and
0 l , eaf ] by Admiral Collinson at a meeting of the Institution,
the 22nd of February, 1861, gives the following account of
the manner in which this running survey was made" On the
British frontier, where it abuts on the Irrawaddy, two boundary
illars are erected; their relative position and distance from each
other has been well ascertained, and the river within this bound
ary has been well surveyed. It was the duty of the surveyors of
the Mission to produce as accurate a survey of the river to the
north of this boundary, within the territories of the King of
Burmah, as the time occupied in the passage of the Mission
allowed them. The principle laid down for the execution of
this duty was a combination of the three elements of time,
speed, and transit bearings ; the result being checked and con
firmed by astronomical observations. The surveyors were well
provided with instruments, and five chronometers were placed
in a cabin of the largest flat, upon a stand purposely erected to
avoid vibration or the effects of concussions, and to give every
facility for winding and comparison. At each end of the roof
of the flat, which was about fifteen feet above the water, and
about 120 feet long, standards were set up to give a line of
sight at right angles to the keel of the vessel. These were
used to ascertain the rate of progress, by noting the interval
between the passing by the two sets of standards of any fixed
object on the bank when the vessel's course was perfectly
straight.f A good prismatic compass was set upon the roof of
the flat, and, starting from a given point, and noting time and
speed, the transit-bearing of every point or object, especially
those on the bank, with every other that was worth remark,
was accurately noted. Objects in the interior were observed
in the same way, and these observations, both backwards and
forwards, were made as numerous as possible, so as to act as
a check one against another. Time of arrival, and speed, at
every point or object before observed, was again noted, the
course being principally along either one bank or the other, to
avoid the extreme strength of the mid-current. The eventual
plotting of the chart was throughout kept constantly in view,
and the connection between all the various objects carefully
preserved. To avoid the errors to which observations of the
# In No. 40, Yol. X. of this Journal, also appears a paper by this officer,
entitled, "Collisions at Sea, and their Remedy by an Improved Sjstem of
Lights."
t This method of computing speed was also adopted by Lieutenants Chippen-
dall, E..E., and Watson, R.E., during their survey of the course of the JSTile
between Khartoum and Rigaf, while employed under Colonel Grordon's orders,
between the 1st of October and the 29th of November, 1874. Lieutenant
Watson describes the method in detail, as though it were a novel one. (See
"Journal of the Royal Geographical Society," vol. xlvi., pp. 412-416.)
VOL. 11. DD