Page:EB1911 - Volume 08.djvu/343

 DIVER, a name that when applied to a bird is commonly used in a sense even more vague than that of loom, several of the sea ducks or Fuligulinae and mergansers being frequently so called, to say nothing of certain of the auks or Alcidae and grebes; but in English ornithological works the term diver is generally restricted to the Family known as Colymbidae, a very well-marked group of aquatic birds, possessing great, though not exceptional, powers of submergence, and consisting of a single genus Colymbus which is composed of three, or at most four, species, all confined to the northern hemisphere. This Family belongs to the Cecomorphae of T. H. Huxley, and is usually supposed to occupy a place between the Alcidae and Podicipedidae; but to which of these groups it is most closely related is undecided. Professor Brandt in 1837 (Beitr. Naturgesch. Vögel, pp. 124–132) pointed out the osteological differences of the grebes and the divers, urging the affinity of the latter to the auks; while, thirty years later, Professor Alph. Milne-Edwards (Ois. foss. France, i. pp. 279–283) inclined to the opposite view, chiefly relying on the similarity of a peculiar formation of the tibia in the grebes and divers, which indeed is very remarkable, and, in the latter group, attracted the attention of Willughby more than 230 years ago. On the other hand Professor Brandt, and Rudolph Wagner shortly after (Naumann’s Vögel Deutschlands, ix. p. 683, xii. p. 395), had already shown that the structure of the knee-joint in the grebes and divers differs in that the former have a distinct and singularly formed patella (which is undeveloped in the latter) in addition to the prolonged, pyramidally formed, procnemial process—which last may, from its exaggeration, be regarded as a character almost peculiar to these two groups. The evidence furnished by oology and the newly-hatched young seems to favour Brandt’s views. The abortion of the rectrices in the gerbes, while these feathers are fairly developed in the divers, is another point that helps to separate the two Families.

The commonest species of Colymbus is C. septentrionalis, known as the red-throated diver from an elongated patch of dark bay which distinguishes the throat of the adult in summer dress. Immature birds want the bay patch, and have the back so much more spotted that they are commonly known as “speckled divers.” Next in size is the black-throated diver, C. arcticus, having a light grey head and a gular patch of purplish-black, above which is a semicollar of white striped vertically with black. Still bigger is the great northern diver, C. glacialis or torquatus, with a glossy black head and neck, two semicollars of white and black vertical stripes, and nearly the whole of the black back and upper surface of the wings beautifully marked with white spots, varying in size and arranged in belts. Closely resembling this bird, so as to be most easily distinguished from it by its yellow bill, is C. adamsi. The divers live chiefly on fish, and are of eminently marine habit, though invariably resorting for the purpose of breeding to freshwater lakes, where they lay two dark brown eggs on the very brink; but they are not unfrequently found far from the sea, being either driven inland by stress of weather, or exhausted in their migrations. Like most birds of their build, they chiefly trust to swimming, whether submerged or on the surface, as a means of progress, but once on the wing their flight is strong and they can mount to a great height. In winter their range is too extensive and varied to be here defined, though it is believed never to pass, and in few directions to approach, the northern tropic; but the geographical distribution of the several forms in summer requires mention. While C. septentrionalis inhabits the north temperate zone of both hemispheres, C. arcticus breeds in suitable places from the Hebrides to Scandinavia, and across the Russian empire, it would seem, to Japan, reappearing in the north-west of North America, though its eastern limit on that continent cannot be definitely laid down; but it is not found in Greenland, Iceland, Shetland or Orkney. C. glacialis, on the contrary, breeds throughout the north-eastern part of Canada, in Greenland and in Iceland. It has been said to do so in Scotland as well as in Norway, but the assertion seems to lack positive proof, and it may be doubted whether, with the exception of Iceland, it is indigenous to the Old World, since the form observed in North-eastern Asia is evidently that which has been called C. adamsi, and is also found in North-western America; but it may be remarked that one example of this form has been taken in England (Proc. Zool. Society, 1859, p. 206) and at least one in Norway (Nyt Mag. for Naturvidenskaberne, 1877, p. 134).

 DIVERS and DIVING APPARATUS. To “dive” (Old Eng. dúfan, dŷfan; cf. “dip”) is to plunge under water, and in the ordinary procedure of swimmers is distinguished from simple plunging in that it involves remaining under the water for an interval of more or less duration before coming to the surface. In the article the sport of diving in this sense is considered. Here we are only concerned with diving as the function of a “diver,” whose business it is to go under water (in modern times, assisted by specially devised apparatus) in order to work.

Unassisted or Natural Diving.—The earliest reference to the practice of the art of diving for a purpose of utility occurs in the Iliad, 16, 745-750, where Patroclus compares the fall of Hector’s charioteer to the action of a diver diving for oysters. Thus it would seem that the art was known about 1000 years before the Christian era. Thucydides is the first to mention the employment of divers for mechanical work under water. He relates that divers were employed during the siege of Syracuse to saw down the barriers which had been constructed below the surface of the water with the object of obstructing and damaging any Grecian war vessels which might attempt to enter the harbour. At the siege of Tyre, divers were ordered by Alexander the Great to impede or destroy the submarine defences of the besieged as they were erected. The purpose of these obstructions was analogous to that of the submarine mine of to-day.

The employment of divers for the salvage of sunken property is first mentioned by Livy, who records that in the reign of Perseus considerable treasure was recovered from the sea. By a law of the Rhodians, their divers were allowed a proportion of the value recovered, varying with the risk incurred, or the depth from which the treasure was salved. For instance, if the diver raised it from a depth of eight cubits (12 ft.) he received one-third for himself; if from sixteen cubits (24 ft.) one half; but upon goods lost near the shore, and recovered from a depth of two cubits (36 in.), his share was only one tenth.

These are examples of unassisted diving as practised by the Ancients. Their primitive method, however, is still in vogue in some parts of the world—notably in the Ceylon pearl fisheries and in the Mediterranean sponge fisheries, and it may, therefore, be as well to mention the system adopted by the natural, or naked, diver of to-day.

The volume and power of respiration of the lungs vary in different individuals, some persons being able to hold their breath longer than others, so that it naturally follows that one man may be able to stay longer under water than another. The longest time that a natural diver has been known to remain beneath the surface is about two minutes. Some pearl and sponge divers rub