elation seems to
be so to manage the two speeds that the angle made by the dredge rope is
fairly constant. This angle can be observed with a simple clinometer.
The following table abridged from Tanner most usefully brings together
the requisite angles with other useful quantities.

+----------+----------------+---------+---------------+---------------+
| Depth of | Speed of ship |Length of|Angle of dredge|Angle of dredge|
| water. | while shooting | rope | rope while | rope while |
| |dredge or trawl.|required.|lowering trawl.|dragging trawl.|
+----------+----------------+---------+---------------+---------------+
| Fathoms. | Knots. | Fathoms.| | |
| 100 | 3 | 200 | 60 | 55 |
| 200 | 3 | 400 | 60 | 55 |
| 400 | 3 | 700 | 60 | 52 |
| 600 | 2-3/4 | 1000 | 55 | 50 |
| 800 | 2-1/2 | 1200 | 50 | 44 |
| 1000 | 2-1/2 | 1500 | 50 | 40 |
| 1500 | 2-1/4 | 2166 | 50 | 40 |
| 2000 | 2 | 2670 | 45 | 35 |
| 3000 | 2 | 4000 | 40 | 35 |
+----------+----------------+---------+---------------+---------------+

The speed of towing, always slow, may be assumed to be approximately
correct if the appropriate angle is maintained. Hauling should at first
be slow from great depths, but may increase in speed as the gear rises.

For further details of deep-sea dredging, especially of the hauling
machinery and management of the gear, the special reports of the
various expeditions must be consulted. Commander Tanner, U.S.N., has
given in _Deep Sea Exploration_ (1897) a very full and good account of
the equipment of an exploring ship; and to this book the present
article is much indebted.

_Modifications and Additions to the Dredge._--From 1818, when Sir John
Ross brought up a fine Astrophyton from over 800 fathoms on a sounding
line in Baffin's Bay, instances gradually accumulated of specimens being
obtained from great depths without nets or traps. The naturalists of the
"Porcupine" and other expeditions found that echinoderms, corals and
sponges were often carried up adhering to the