d with a pendulum made to swing
half-seconds. It was a musket ball slung with twine, and measured 9.8
inches from the fixed end of the twine to the centre of the ball. From
the instant that the flash of the first gun was perceived to the time of
hearing the report I counted eighty-five vibrations of the pendulum, and
the same with two succeeding guns; whence the length of the base was
deduced to be 8.01 geographic miles.* A principal station in the survey
of Port Lincoln was a hill on the north side called _Northside Hill_,
which afforded a view extending to Sleaford Mere and Bay and as far as
Cape Wiles on one side, and to the hills at the beak of Coffin's Bay on
the other. A great part of the bearings taken from hence crossed those
from Stamford Hill very advantageously.

[* This length was founded on the supposition, that sound travels at the
rate of 1142 feet in a second of time, and that 6060 feet make a
geographic mile. A base of 15' 24" of latitude was afterwards obtained
from observations in an artificial horizon, and of 25' 17" of longitude
from the time keepers with new rates, both correct, as I believe, to a
few seconds. From this long base and theodolite bearings, the first base
appeared to be somewhat too short; for they gave it 8.22 instead of 8.01
miles. The length of the pendulum in the first measurement was such as to
swing half seconds in England; and I had not thought it, in this case,
worth attention, that by the laws of gravity and the oblate spheroid, the
pendulum would not swing so quick in the latitude of 35 deg.. I must leave it
to better mathematicians to determine from the _data_ and the true length
of a geographic mile in this latitude, whether the base ought to have
been 8.22 as given by the observations and bearings: it was proved to be
sufficiently near for all the purposes of a common nautical survey.]

Amongst the various excursions made by the scientific gentlemen, one was
directed to Sleaford Mere, of which they made the circuit. The two
southern branches were found to terminate within a hundred yards of the
head of Sleaford Bay, with which the mere had been suspected to have a
communication from its water being not quite fresh; but they are
separated by a stony bank too high for the surf ever to pass over it. At
the head of the bay a boat's sail and yard were seen floating, and no
doubt had belonged to our unfortunate cutter: after being set out to sea
by the tide, it had been driven