TKANSACTIONS OK SECTION D. 633 



do not seem to be eaten by other animals, we have at once an explanation of their 

 fearless habits and of their conspicuous appearance. The brilliant colours are in 

 this case of a warning nature, lor the purpose of rendering the animal provided 

 with the stinging cells noticeable and recognisable. 



These, then, are the grounds upon which 1 base my view that the chief function 

 of the cerata is by varied shapes and colours to enable the animals to assume pro- 

 tective or warning appearances as may be found best suited to their surroundings 

 and mode of life. 



7. On the Electric Light as a means of attracting Marine Animals. 

 By Professor W. A. Herdman, B.Sc, F.L.S. 



Since the publication in ' Nature ' for June 7, 1888, of the chief results obtained 

 by the use of the submarine electric light during one of the Liverpool Alarine 

 Biology Committee's dredging expeditions, I have received a number of inquiries 

 from biologists, fishermen, and others as to the details of the apparatus used, and 

 the exact method of illuminating the tow-nets. Consequently, I believe, it may be 

 useful if I lay before this meeting a brief statement of how the electric light has 

 been employed up to the present time in marine biology, and with what results. 



The first application of this important method of collecting appears to have 

 been made by the United States Fish Commission in 1884,' on board the steamer 

 Albatross. On that occasion an arc lamp was merely suspended above the surface 

 of the water, and it was found to attract Araphipods, Squids, and young fish to the 

 surface. In the following year the same naturalists experimented further by 

 lowering an Edison incandescent lamp - into the water, with similar good results. 

 The Fish Commission do not give any details in regard to the animals collected, 

 nor any comparison between the contents of illuminated and ordinary tow-nets 

 worked at the same time. 



The next submarine electric light experiments were those carried out by the 

 Liverpool Marine Biology Committee in May 1888, on board the steamer Hymna 

 during a three-days' dredging expedition in the Irish Sea. The liyana, kindly lent 

 by the Liverpool Salvage Association, is provided, for wrecking purposes, with the 

 following electric light installation : ^ — A Gwynne vertical engine, of 6 nominal 

 h.p., running at 300-400 revolutions per minute, works a Phoenix compound 

 wound dynamo, with an effective output of 5,980 Watts (fi5 volts 92 amperes), 

 at LOOO revolutions per minute. There are two Pilsen arc lamps of 3,000 

 nommal c.p. each, which can be used on deck or at masthead or on the side of the 

 ship ; four Edison-Swan submarine incandescent lamps of 100 c.p., and ten of 16 

 cp. each. The dynamo, being compounded, allows the arc and incandescent lamps 

 to be nm together with perfect ease by the use of a resistance of about "5 of an 

 ohm in the arc-light circuit. The submarine lamps are fitted in strong circular 

 annealed glass protectors, and can be lowered to any required depth in the water 

 by means of a special waterpoof flexible cable, made of 260 strands of fine copper 

 wire, covered with thick guttapercha and hemp. The arc lamps require from 

 25-30 amperes, and the submarine lamps 4'6 amperes, so that there is ample power 

 when the whole installation is running. 



This apparatus was first used for biological purposes in Ramsey Bay on the first 

 night of the cruise. After dark one of the large arc lamps was hoisted a few feet 

 above deck, so as to allow work to be carried on almost as easily as during the day. 

 We then arranged one of the submarine incandescent lamps in the mouth of a tow- 

 net 80 as to be just well within the iron ring, and yet not too deeply in the net, 

 the object being to illuminate the entrance to the net and not the middle or tail 

 end. This illuminated net was let down to a depth of three fathoms, and at the 

 same time another tow-net without any light was let down to the same depth 



' Hull. U. S. Fhh Commission, vol. iv., p. 153. 

 ' Zoc. cit. vol. v., p. 464. 



' I am indebted to Captain Young, of the Liverpool Salvage Association, for this 

 information in regard to the plant on board the Hycena. 



