634 REPOKT— 1889. 



OTer the other side of the ship. When, after half an hour, the nets were 

 hauled in, as the one with the electric light approached the surface numerous small 

 Crustacea were noticed accompanying it, and darting about in the bright light. 

 This tow-net, when emptied into a glass jar of sea-water, was found to have con- 

 tained an abundant gathering, consisting mainly of Crustaceans, while the net in 

 the dark on the other side of the ship had practically nothing. The two nets were 

 then put out again, this time to a depth of six fathoms, and at a greater distance 

 from one another, with the same general results as before. These two experiments 

 showed pretty conclusively the effect of the brilliant light in attracting the free- 

 swimming animals, the difference between the contents of the two nets being on 

 both occasions most marked. Consequently, on the second night, in Port Erin 

 Bay, both nets were illuminated, and, while the one was let down close to the 

 bottom at a depth of 5 fathoms, the other was kept at the surface. This experi- 

 ment was tried three times, with the same result each time. Both nets contained 

 abundance of animals, but the bottom and surface gatherings differed greatly in 

 appearance and in constitution — the net from the bottom containing mainly large 

 Amphipoda and Oumacea, while that from the surface was characterised by the 

 abundance of Copepoda. For further details as to the species obtained in these 

 various gatherings I must refer to the article in ' Nature,' "^ and to the reports 

 in the ' Fauna of Liverpool Bay,' vol. 2 ; on the Copepoda, by Mr. I. C. Thompson ; 

 and on the other Crustacea, by Mr. A. 0. Walker. 



During June of the same summer (1888) Prince Albert of Monaco - used on 

 board his yacht Hirundelle a tow-net lit by a small incandescent lamp, supplied by 

 a single Bunsen cell (in which the nitric acid is replaced by chromic acid). 



The battery, which was let down into the sea along with the net, is hermetically 

 sealed up in an iron case, while, when the apparatus is used in great depths, the 

 pressure is ingeniously equalised by a tube connecting the interior of the case with 

 a strong indiarubber ball filled with air. This apparatus was tried in the neigh- 

 bourhood of the Azores, down to a depth of about 20 fathoms, but apparently 

 without much success. 



In April 1889 the steamer Hymna was again placed at the service of the Liver- 

 pool Marine Biologjr Committee for a five days' cruise,^ and the opportimity was 

 taken advantage of to make a further series of experiments with nets illuminated 

 by the electric light. On two successive nights in Port Erin Bay, after dark, both 

 the large arc lamps were lit up and were suspended half-mast high, so as to throw 

 a strong glare upon the water at the sides of the vessel. Tow-nets provided with 

 submarine lamps were then used both at the bottom (six fathoms) and at the surface, 

 and an ordinary tow-net was dragged by Mr. 1. C. Thompson round and round the 

 ship in the brightly-illuminated water. All of these nets gave abundant gatherings, 

 consisting mainly of Copepoda, Amphipoda, Schizopoda, and Cumacea, and differing 

 most markedly from the gatherings taken in the same spot during the daytime with- 

 out the electric light. In this case there was no difference noticed between the con- 

 tents of the bottom and of the surface nets, both containing abundance of Oumacea. 

 This difference from the previous year's results was probably due, 1 think, to our 

 having a much more powerful surface light (6,000 c.p.\ which had been shining for 

 at least half an hour before the tow-nets were put over, with the result that the 

 Oumacea and other bottom Crustacea were attracted to the surface from a depth 

 of six fathoms. On the last day of the cruise we took a gathering successfully with 

 an illuminated tow-net from a depth of 30 fathoms, the deepest water on our course 

 from the Isle of Man to Liverpool. 



The results of these experiments in Liverpool Bay have been such as to show 

 conclusively that the submarine electric light is an important addition to the 

 collecting methods of the marine biologist, and one which ought certainly to come 

 into extensive use in the future. It is, of course, only very rarely that a vessel like 

 the Hymna, so fitted up that the electric light can be turned on readily at any time 



' Nature, vol. xxxiii., June 7, 1888. 



^ Comptes-rendus, t. cvii., July 9, 1888. 



^ For the general results of this cruise see Nature, May 9, 1889. 



