144 A VOYAGE TO [South Coast 
Februa W °° d at SU ° h timGS aS the pitS might re( I uire to be left f °r replen- 
e luary ' ishing. 
The necessary duties being all set forward under the superin- 
tendance of proper officers, I employed the following days in survey- 
ing and sounding. The direction of the port was too remote from the 
meridian to obtain a base line from differences of latitude, which, 
when observed in an artificial horizon, and at stations wide apart, I 
consider to be the best; nor was there any convenient beach or open 
place where a base line could be measured. It was therefore 
attempted in the following manner : Having left orders on board the 
ship to fire three guns at given times, I went to the south-east end 
of Boston Island, 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 North- 
side 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 
* 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 firsHjase appeared to be 
somewhat too short; for they gave it 8,22 instead of 8,01 miles. The length of the pen- 
dulum 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°. 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 observa- 
tions and bearings: it was proved to be sufficiently near for all the purposes of a common 
nautical survey. 
