HARDWICKE'S SCIENCE-GOSSIP. 



20I 



of science when Dr. Robert Ball invented the 

 naturalist's dredge. By its use, a great part of 

 our present knowledge concerning the varieties and 

 numbers of the inhabitants of the ocean's depths 

 was gained. 



Previously to this, naturalists availed themselves of 

 the huge ungainly apparatus which fishermen used 

 for obtaining oysters and scallops. This consisted of 

 a large, heavy, single-bladed frame, and a bag formed 

 of iron rings, after the fashion of the ancient chain- 

 mail. The meshes of the net were large, in order 

 that only oysters of a marketable size might be retained ; 

 thus other animals of considerable dimensions alone 

 could be obtained by its use. 



Ball's dredge is a much smaller and more portable' 

 affair, the scraping blades being double, and the bag 

 composed of strongly-netted twine. 



It was with such dredges that the late Sir Wyville 

 Thomson did so much in the Natural History 

 department of the famous "Challenger'-' Expedition. 



Owing to the enormous depths at which he used 



When dredging at greater depths, the weight may 

 be increased if desirable, by attaching heavy sinkers to 

 the rope, a short distance in front of the bridles. 



The general appearance of such a dredge is seen 

 from the sketch below. 



It was with such a dredgo that Mr. P. H. Gosse, 

 the author of the Manual of " Marine Zoology for the 

 British Isles," made so many discoveries in that 

 subject, and to the productions of which, doubtless, 

 we owe the writing of his numerous popular works 

 on marine fauna. 



Of all pastimes open to the young naturalist, that 

 of dredging ranks pre-eminent. This is so, not only 

 on account of the exercise involved in, or the health 

 gained by its pursuit, but from the very beauti- 

 ful and rare nature of its production. During the 

 summer months, much amusement and instruction is 

 to be gained by the dredge, at any of our watering 

 places, and by those in the vicinity of the Frith of 

 Clyde. 



Let the reader accompany us on a dredging 



Fig. 1 1 6. — Dredge, showing its position on the ground. 



them, his dredges were necessarily very heavy and 

 powerful ones. The weight of the smallest was 20 lbs. 



Such a heavy dredge, it is apparent, could only be 

 used from steamships or large vessels, and thus would 

 hardly meet the requirements of the amateur marine 

 zoologist. What the latter needs is a dredge at once 

 so portable, that it may be with ease carried under the 

 arm ; and suitable for the lugsail, or ordinary rowing 

 boat. These requirements are, I think, fully met by 

 a dredge of the following dimensions : — 



Galvanised iron frame, 18 inches by 45 ; double 

 bridles on each side, 2 feet long ; scraping blades, 

 2 inches broad ; netted bag, about 2 feet deep. 

 The bridles, attached to the cross-bars of the frame 

 by means of eyes, are movable, thus allowing them 

 to be folded down upon one another, when not in use. 

 The meshes of the bag may be half an inch in dia- 

 meter, except at the bottom, where it is well to have 

 them considerably smaller. 



The whole apparatus weighs only 5^ lbs. ; and this 

 at a depth of twenty or thirty fathoms, with forty 

 fathoms of rope, is a load quite as heavy as the 

 ordinary single rower can manage. 



excursion. Let us see what is to be scraped up 

 from the bottom of the Frith of Clyde. 



A calm day being chosen, we start away in a 

 rowing boat — let us say from Dunoon. 



At about a hundred and fifty yards from the shore 

 we throw out the dredge. The depth here is from 

 eight to ten fathoms ; so, to ensure the dredge biting 

 properly, about twenty fathoms of rope must be let 

 out. The longer the rope, the deeper the blade of 

 the dredge scrapes, due to the angle it makes with 

 the bottom being more an acute one. 



To dredge properly the net should glide along the 

 bottom, and not dip too deeply into it. The bottom 

 most easy for dredging is one of gravel ; a sandy 

 one is more difficult, and a muddy or clayey bed 

 almost out of the question. Tliat most productive of 

 good specimens is probably a mixture of gravel and 

 sand with patches of seaweed. The distance tra- 

 versed in a given time will of course vary with the 

 nature of the bottom. Having rowed the boat for 

 about ten or fifteen minutes, let us pull our dredge on 

 board. Up it comes, with the mouth of the net 

 clogged with masses of dripping seaweed. Chief 



