It is a
discovery which, like others of no less scientific importance, has
arisen, incidentally, out of work devoted to very different and
exceedingly practical interests.
When men first took to the sea, they speedily learned to look out for
shoals and rocks; and the more the burthen of their ships increased,
the more imperatively necessary it became for sailors to ascertain with
precision the depths of the waters they traversed. Out of this
necessity grew the use of the lead and sounding line; and, ultimately,
marine-surveying, which is the recording of the form of coasts and of
the depth of the sea, as ascertained by the sounding-lead, upon charts.
At the same time, it became desirable to ascertain and to indicate the
nature of the sea-bottom, since this circumstance greatly affects its
goodness as holding ground for anchors. Some ingenious tar, whose name
deserves a better fate than the oblivion into which it has fallen,
attained this object by "arming" the bottom of the lead with a lump of
grease, to which more or less of the sand or mud, or broken shells, as
the case might be, adhered, and was brought to the surface. But, however
well adapted such an apparatus might be for rough nautical purposes,
scientific accuracy could not be expected from the armed lead, and to
remedy its defects (especially when applied to sounding in great depths)
Lieut.
Pages:
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101