running title has been affixed to all the pages; on one side is expressed
the country or coast, and on the opposite the particular part where the
ship is at anchor or which is the immediate subject of examination; this,
it is hoped, will answer the main purpose of an index, without swelling
the volumes. Longitude is one of the most essential, but at the same time
least certain _data_ in hydrography; the man of science therefore
requires something more than the general result of observations before
giving his unqualified assent to their accuracy, and the progress of
knowledge has of late been such, that a commander now wishes to know the
foundation upon which he is to rest his confidence and the safety of his
ship; to comply with this laudable desire, the particular results of the
observations by which the most important points on each coast are fixed
in longitude, as also the means used to obtain them, are given at the end
of the volume wherein that coast is described., as being there of most
easy reference.

The deviations in the Atlas from former practice, or rather the
additional marks used, are intended to make the charts contain as full a
journal of the voyage as can be conveyed in this form; a chart is the
seaman's great, and often sole guide, and if the information in it can be
rendered more complete without introducing confusion, the advantage will
be admitted by those who are not opposers of all improvement. In closely
following a track laid down upon a chart, seamen often run at night,
unsuspicious of danger if none be marked; but some parts of that track
were run in the night also, and there may consequently be rocks or
shoals, as near even as half a mile, which might prove fatal to them; it
therefore seems proper that night tracks should be distinguished from
those of the day, and they are so in this Atlas, I believe, for the first
time. A distinction is made between the situations at noon where the
latitude was observed, and those in which none could be obtained; and the