THE DEPTHS OF THE OCEAN.*
THESE two volumes, both dealing with the same subject from different aspects, dwell upon the comparative slightness of the knowledge which we have of the bottom of the sea and the plant and animal life which inhabits the oceans. Both volumes also show the immense improvements in the methods and machinery of exploration since the days of the 'Challenger' expedition with which Sir John Murray was connected. But if our knowledge of oceanography is comparatively speaking in its infancy, one must not forget the difficulties that attend it. It has been said that studying the depths of the ocean is like hovering in a balloon high above an unknown land which is hidden by clouds. We can have no complete picture. We must patiently put together a mosaic from the scanty material that we dredge from the unseen depths. So progress is dependent on improved mechanical appliances. Of these one of the greatest is the substitution of wire for hemp lines in sounding and dredging. But with every improvement the difficulty remains that one cannot see the apparatus at work ; and when, after perhaps hours of hauling, the complicated appliance comes up empty on to the deck, the workers can only guess whether there was nothing to catch, whether it has never reached the bottom, or whether it has failed to act. Where so much scientific work remains to be done and so great additions to our knowledge may be expected, it is surprising that more rich men are not tempted to emulate the Prince of Monaco. The second and the smaller of the two volumes before us, Science of the Sea, is described as an elementary handbook of practical oceanography for travellers, sailors, and yachtsmen. It aims (having been prepared by the 'Challenger' Society f,a- the study of oceanography) at instructing the few naval • (1) The Depths of the Ocean. By Sir John Murray, K.C.B., F.B.S., and Dr. Johan Hjort. With contributions from Prof. A. Appellof, Prof. H. H. Oran, and Dr. B. Helland-Hansen. London : Macmillan and Co. [Ms. net.]— (2) Science of the Sea. Prepared by the Challenger Society, and edited by G. Herbert Fowler, B.A., Ph.D., F.L.S. With illustrations and charts. London: John Murray. Ps. net.]
officers, yacht-owners, and merchant-captains who take any interest in natural science what they should observe and collect when they are at sea. The practical part of the book which deals with methods of obtaining and preserving marine plants and animals is extremely good. If the volume has a defect it is that it attempts inevitably to cover too much ground and assumes a knowledge of biology which perhaps few who use it will possess. Still, the main object of the book, which is to teach how to observe, to collect, to preserve, to label, to keep notes, and to make records, is successfully carried out. Each chapter is by an authority qualified to instruct. The chapters deal with the air, the water, shore collecting, plants (floating and fixed), animals (of the sea- Boor and floating), yacht equipment, dredging, trawling and fishing, logs, notes, and labels. It will be seen that the whole subject of oceanography is touched on. There are also useful lists of marine stations, of books of reference, of firms who supply appliances, and also many figures.
We turn now to the large, profusely illustrated, and some- what heavy volume, The . Depths of the Ocean, in writing which Sir John Murray and Dr. Hjort, the Director of Norwegian Fisheries, have been assisted by other Norwegian men of science. If any parts of the work have been trans- lated, the English is excellent. The book is based largely on the researches made by the Michael Sara,' a Norwegian steamer which, after working diligently for ten years in Norwegian seas, was despatched in 1910 on a five months' tour across the Atlantic and back. The cost of the expedition was munificently borne by Sir John Murray. The collections have gone to Bergen, and the authorities of that museum will in due course publish their detailed scientific reports of the voyage. The book gives, besides, a general account of our present knowledge of the sea bottom and the life that inhabits it. It gives also an historical review of the progress that has been made since 1504, when soundings first appeared on Juan de la Cosa's maps. We do not know any other book where a read- able and semi-popular survey of oceanography can be found. The present volume, like the last, tries to cover a great deal of ground, but it does so effectively, and contains a mass of in- formation on the fauna and flora of the deep sea especially. It is difficult to remember that about two-thirds of the sea-bottom are covered by more than 2,000 fathoms of water, and that a dark abyss covers ninety millions of square miles, or nearly half the surface of our planet. The plants are confined to regions where sunlight penetrates, but blind and phosphorescent fishes and other marine animals have been obtained from enormous depths. On two matters the cruise of the Michael Sara' has added to what we know: one is the penetration of light into the ocean and the other is the vertical distribution of fishes on which our knowledge is still imperfect. At about 500 fathoms the influence of sunlight could still be traced on photographic plates, but at about 800 fathoms no influence could be detected. Long before that depth we come to a region inhabited by black fishes and red crustaceans.
Since all the animals of the sea ultimately depend for their food on plants it is hard to understand how all the animals get enough nourishment. The diatoms and other floating microscopic plants are mostly consumed by copepods, whe in their turn furnish food for other larger creatures, until we get whales devouring the giant cephalopods. It seems to be established, as regards northern seas, that on an average 56 per cent, of the plankton, or floating organisms, of the sea are plants and 44 per cent. are animals. There are good chapters in this book on pelagic plant life by Professor Gran and pelagic animal life by Dr. Hjort; unfortunately they are both rather beyond the general reader. But the book has a wide scope, and both in the figures of marine animals and in the earlier chapters there is much of general interest.
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