DREDGING AT ORAN. 
55 
dredge, as a provision for keeping tlie dredge-net always extended to 
its full length, and for preventing any risk of the tangles or the end of 
the net getting folded over the mouth of the net, and so causing the 
dredge to come up empty. In the experience of the Oban dredging 
such accidents occasionally happened, and the adoption of a similar 
precaution in future is desirable. 
Another point in which the working of the present dredge was not 
satisfactory is, that the dredge came up on several occasions only very 
imperfectly filled, and appeared to have not been dragged properly 
along the sea bottom, and to have been lifted off the bottom by the 
oblique pull of the rope. In the “ Challenger ” deep-sea dredging, 
where the difficulty from this cause was enormously increased by the 
dredging being carried to a depth of from 2^ to miles, a special con¬ 
trivance was used for overcoming this difficulty, and a weight of 1J cwt. 
was attached to the rope at 200 to 500 fathoms’ distance in advance of the 
dredge (or a distance equal to about l-8th of the depth being dredged). 
This “messenger ” weight trailed along the sea bottom, and caused 
the pull upon the dredge to be under all circumstances in a direction 
parallel to the bottom and close down upon the ground, thus keeping 
the dredge at all times in the best position for its work. As a con¬ 
sequence of this arrangement, the risk was somewhat increased of the 
dredge getting jammed by some obstruction at the bottom, and when¬ 
ever that occurred it became necessary to ease the rope by letting it 
slip for a certain distance, until the steamer could be backed over the 
dredge in order to clear it from the obstruction. The circumstance of 
the dredge becoming jammed was instantly ascertained by means of a 
spring-tension apparatus in the hauling tackle, the guiding pulley over 
which the rope was led to the dredge being suspended by a set of 80 
strong india-rubber bands (similar to door springs), which were 
capable of stretching as much as 14ft. before reaching the strain at 
which the rope would break (24 tons) ; and due warning was thus given 
by a sudden increased stretch taking place whenever the dredge got 
fast. In the Oban dredging this object was aimed at b}^ feeling the ten¬ 
sion of the rope by hand from time to time, to detect any undue 
resistance, and also to ascertain whether the resistance was sufficient 
for indicating that the dredge was dragging properly on the ground. 
In order to prevent the injury of the specimens by the scraping lip of 
the net striking them before they can be caught by the tangles, it appears 
requisite for the tangles to be fixed separately farther up the rope in ad¬ 
vance of the net, so that when the dredge is dragged along, the bottom 
shall be first Uijhtly swept by the tangles before being scraped by the 
dredge ; and it is also requisite that the cross-bar carrying the tangles 
shall not itself drag upon the ground so as to cause similar mischief to 
that previously done by the dredge scraper, but shall be propped up 
sufficiently high above the ground to prevent this, but not so high as 
to risk the tangles floating clear off the ground. 
It is now' suggested that the above objects, and also the other re¬ 
quirement of a “messenger” w'eight in advance of the dredge for 
