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Encyclopedia Britannica - Main :: SUS-TAV |
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SWAN, SIR JOSEPH WILSON (1828 ) , English physicist and electrician, was born at Sunderland on the 31st of October 1828. After serving his apprenticeship with a chemist in his native town, he became first assistant and later partner in a firm of manufacturing chemists in Newcastle. Among its operations this firm included the manufacture of photographic plates, and thus Swan was led to one of the advances in photography with which his name is associatedthe production of extremely rapid dry plates, which were the outcome of an original
wash
paper by means of indiarubber solution, and then detaching the original
paper or card with charcoal powder in a crucible and subjecting the whole to a high temperature. The carbonized paper thus obtained he mounted in the form of a fine strip in a vacuous glass vessel and connected it with a battery of Grove's cells, which though not strong enough to raise it to complete incandescence, were sufficient to make it red-het. This was substantially the method adopted by Edison nearly twenty years later, after various fruitless efforts to make a practical lamp with a filament of platinum or a platinum alloy had convinced him of the unsuitability of that metal for the purposea conclusion which Swan had reasoned out for himself many years before. By the time Edison had hit upon the idea of carbonizing paper or bamboo by heat to form the filament, Swan had devised the further improvement of using cotton
and literature. Scientifically it is usually known as Cygnus olor. Its large size, its spotless white plumage, its orange-red bill, surmounted by a black knob (technically the "berry ") larger in the male than in the female, its black legs and stately appearance on the water are familiar, either from figures innumerable or from direct observation, to almost every one. When left to itself its nest is a large mass of aquatic plants, often piled to the height of a couple of feet and possibly some six feet in diameter . In the midst of this is a hollow which contains the eggs, generally from five to nine in number, of a greyish-olive colour. The period of incubation is between five and six weeks, and the young when hatched are clothed in sooty-grey down, which is succeeded by feathers of sooty-brown. This suit is gradually replaced by white, but the young birds are more than a twelve-month old before they lose all trace of colouring and become wholly white.It was, however, noticed by Plot (N.H. Staffordshire, p. 228) more than 20o years ago that certain swans on the Trent had white cygnets; and it was subsequently observed of such birds that both parents and progeny had legs of a paler colour, while the young had not the " blue bill " of ordinary swans at the same age that has in some parts of the country given them a name, besides offering a few other minor differences. These, being examined by W. Yarrell led him to announce (Proc. Zool. Society, 1838, p. 19) the birds presenting them as forming a distinct species, C. immutabilis, to which the English name of " Polish " swan had already been attached by the London poulterers,) but which is now regarded merely as a variety, not in any way specially associated with Poland but possibly a dimorphic form.The whooper, whistling or wild swan2 of modern usage, Cygnus musicus, which was doubtless always a winter-visitant to Britain, though nearly as bulky and quite as purely white in its adult plumage, is at once recognizable from the species which has been half domesticated by its wholly different but equally graceful carriage, and its billwhich is black at the tip and lemon-yellow for a great part of its base. This entirely distinct species is a native of Iceland, eastern Lapland and northern Russia, whence it wanders southward in autumn, and the musical tones it utters (contrasting with the silence that has caused its relative to be often called the mute swan) have been celebrated from the time of Homer to our own. Otherwise in a general way there is little difference between the habits of the two, and very closely allied to the whooper is a much smaller species, with very well marked characteristics, known as Bewick's Swan, C. bewicki. This was first indicated as a variety of the last by P. S. Pallas, but its specific validity is now fully established. Apart from size, it may be externally distinguished from the whooper by the bill having only a small patch of yellow, which inclines to an orange rather than a lemon tint; while internally the difference of the vocal organs is well marked, and its cry, though melodious enough, is unlike. It has a more easterly home in the north than the whooper, but in winter not infrequently occurs in Britain. Both the species last mentioned have their representatives in North America, and in each case the transatlantic bird is considerably larger than that of the Old World. The first is the trumpeter-swan, C. buccinator, which has the bill wholly black, and the second the C. columbianusgreatly resembling Bewick's swan, but with the coloured patches on the bill of less extent and deepening almost into scarlet. South America produces two very distinct birds commonly regarded as swans, Cygnus melanocoryphus, the black-necked swan, and that which is called Coscoroba. This last, C. candida, which inhabits the southern extremity of the continent to Chile and the Argentine territory and visits the Falkland Islands, is the smallest species knownpure white in colour except the tip of its primaries, but having a red bill and red feet.3 The former, if not discovered by earlier navigators, was M. Gerbe, in his edition of Degland's Ornithologie Europeenne (ii. 477), makes the amusing mistake of attributing this name to the fourreurs (furriers) of London, and of reading it Cygne du pole (polar, and not Polish, swan)! 2 In some districts it is called by wild-fowlers " elk," which perhaps may be cognate with the Icelandic Alit and the Old German Elbs or Elps (cf. Gesner, Ornithologia, pp. 358, 359), though by modern Germans Etb-schwan seems to be used for the preceding species. 3 Dr Stejneger (Proc. U. S. Nat. Museum, 1882, pp. 177179) has been at much pains to show that this is no swan at all, but merely a large Anatine form. Further research may prove that his views are well founded, and that this, with another very imperfectly known species, C. davidi, described by Swinhoe (Proc. Zool. Soc.,observed by Narbrough on the 2nd of August 1670 in the Strait of Magellan, as announced in 1694 in the first edition of his Voyage (p. 52). It was subsequently found on the Falkland Islands during the French settlement there in 17641765, as stated by Pernetty (Voyage, 2nd ed., ii. 26, 99), and was first technically described in 1782 by Molina (Saggio sulla star. nat. del Chile, pp. 234, 344). Its range seems to be much the same as that of the Coscoroba, except that it comes farther to the northward, to the coast of southern Brazil on the east, and perhaps into Bolivia on the west. It is a very handsome bird, of large size, with a bright red nasal knob, a black neck and the rest of its plumage pure white. It has been introduced into Europe, and breeds freely in confinement.A greater interest
chief
The Cygninae admittedly form a well-defined group of the family Anatidae, and there is now no doubt as to its limits, except in the case of the Coscoroba above mentioned. This bird would seem to be, as is so often found in members of the South American fauna, a more generalized form, presenting several characteristics of the Anatinac, while the rest, even its black-necked compatriot and the almost wholly black swan of Australia, have a higher morphological rank. Excluding from consideration the little-known C. davidi, of the five or six species of the northern hemisphere four present the curious character, somewhat analogous to that found in certain cranes (q.v.), of the penetration of the sternum by the trachea nearly to the posterior end of the keel, whence it returns forward and upward again to revert and enter the lungs; but in the two larger of these species, when adult, the loop of the trachea between the walls of the keel takes a vertical direction, while in the two smaller the bend is horizontal
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