Page:EB1911 - Volume 08.djvu/585

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562
DREDGE AND DREDGING


place after meals, the remainder being supernatural. Cicero, however, takes the view that they are simply natural occurrences no more and no less than the mental operations and sensations of the waking state. The pathological side of dreams attracted the notice of physicians. Hippocrates was disposed to admit that some dreams might be divine, but held that others were premonitory of diseased states of the body. Galen took the same view in some of his speculations.

Symbolical interpretations are combined with pathological no less than animistic interpretations of dreams; they are also extremely common among the lower classes in Europe at the present day, but in this case no consistent explanation of their importance for the divination of future events is usually discoverable. Among the Greeks Plato in the Timaeus (ch. xlvi, xlvii) explains dreams as prophetic visions received by the lower appetitive soul through the liver; their interpretation requires intelligence. The Stoics seem to have held that dreams may be a divine revelation and more than one volume on the interpretation of dreams has come down to us, the most important being perhaps the Όνειροκριτικά of Daldianus Artemidorus. We find parallels to this in a Mussulman work by Gabdorrachaman, translated by Pierre Vattier under the name of Onirocrite mussulman, and in the numerous books on the interpretation of dreams which circulate at the present day. In Siam dream books are found (Intern. Archiv für Anthr. viii 150); one of the functions of the Australian medicine man is to decide how a dream is to be interpreted.

Modern Views.—The doctrine of Descartes that existence depended upon thought naturally led his followers to maintain that the mind is always thinking and consequently that dreaming is continuous. Locke replied to this that men are not always conscious of dreaming, and it is hard to be conceived that the soul of the sleeping man should this moment be thinking, while the soul of the waking man cannot recollect in the next moment a jot of all those thoughts. That we always dream was maintained by Leibnitz, Kant, Sir W. Hamilton and others; the latter refutes the argument of Locke by the just observation that the somnambulist has certainly been conscious, but fails to recall the fact when he returns to the normal state.

It has been commonly held by metaphysicians that the nature of dreams is explained by the suspension of volition during sleep; Dugald Stewart asserts that it is not wholly dormant but loses its hold on the faculties, and he thus accounts for the incoherence of dreams and the apparent reality of dream images.

Cudworth, from the orderly sequence of dream combinations and their novelty, argues that the state arises, not from any “fortuitous dancings of the spirits,” but from the “phantastical power of the soul.” According to K. A. Scherner, dreaming is a decentralization of the movement of life; the ego becomes purely receptive and is merely the point around which the peripheral life plays in perfect freedom. Hobbes held that dreams all proceed from the agitation of the inward parts of a man’s body, which, owing to their connexion with the brain, serve to keep the latter in motion. For Schopenhauer the cause of dreams is the stimulation of the brain by the internal regions of the organism through the sympathetic nervous system. These impressions the mind afterwards works up into quasi-realities by means of its forms of space, time, causality, &c.

Bibliography.—For full lists of books and articles see J. M. Baldwin’s Dictionary of Philosophy, bibliography volume (1906), and S. de Sanctis, I Sogni, also translated in German with additions as Die Träume. Important works are—Binz, Über den Traum, Giessler Aus den Tiefen des Traumlebens, Maury, Le Sommeil et les rêves, Radestock, Schlaf und Traum, Tessié, Les Rêves, Spitta, Schlaf und Traumzustande. For super-normal dreams see F. W. H. Myers, Human Personality, vol i, and Proc S P R viii 362. For voluntary dreams see Proc. S P R iv 241, xvii. 112. On prophetic dreams see Monist, xi 161, Bull. Soc. Anth. (Paris, 1901), 196, (1902), 228, Rev. de synthèse historique (1901), 151, &c. On incubation see Deubner, De incubatione, Maury, La Magie. On the dreams of American Indians see Handbook of American Indians (Washington, 1907), s v “Dreams” and “Manito.” On the interpretation of dreams see Freud, Die Traumdeutung. Other works are F. Greenwood, Imagination in Dreams, Hutchinson, Dreams and their Meanings.

 (N. W. T.) 


DREDGE and DREDGING. The word “dredge” is used in two senses. (1) From Mid. Eng. dragie, through Fr. dragée, from Gr. τραγήματα, sweetmeats, it means a confection of sugar formed with seeds, bits of spice or medicinal agents. The word in this sense is obsolete, but survives in “dredger,” a box with a perforated top used for sprinkling such a sugar-mixture, flour or other powdered substance. “Dredge” is also a local term for a mixed crop of oats and barley sown together (“maslin” or “meslin,” cf. Fr. dragée), and in mining is applied to ore of a mixed value. (2) Connected with “drag,” or at least derived from the same root, dredge or dredger is a mechanical appliance for collecting together and drawing to the surface (“dredging”) objects and material from the beds of rivers or the bottom of the sea. In the following account the operations of dredging in this sense are discussed (1) as involved in hydraulic engineering, (2) in connexion with the work of the naturalist in marine biology.


1. Hydraulic Engineering


Dredging is the name given by engineers to the process of excavating materials under water, raising them to the surface and depositing them in barges, or delivering them through a shoot, a longitudinal conveyor, or pipes, to the place where it is desired to deposit them. It has long been useful in works of marine and hydraulic engineering, and has been brought in modern times to a state of high perfection.

The employment of dredging plant and the selection of special appliances to be used in different localities and in varying circumstances require the exercise of sound judgment on the part of the engineer. In rivers and estuaries where the bottom is composed of light soils, and where the scour of the tide can be governed by training walls and other works constructed at reasonable expense, so as to keep the channel clear without dredging, it is manifest that dredging machinery with its large cost for working expenses and for annual upkeep should be as far as possible avoided. On the other hand, where the bottom consists of clay, rock or other hard substances, dredging must, in the first instance at any rate, be employed to deepen and widen the channel which it is sought to improve. In some instances, such as the river Mississippi, a deep channel has for many years been maintained by jetties, with occasional resort to dredging to preserve the required channel section and to hasten its enlargement. The bar of the river Mersey is 11 m. from land, and the cost of training works would be so great as to forbid their construction; but, by a capital expenditure of £120,000 and an annual expense of £20,000 for three years, the depth of water over the bar at low tide has been increased by dredging from 11 ft. to 27 ft., the channel being 1500 ft. wide.

”Bag and Spoon” Dredger.—The first employment of machinery for dredging is, like the discovery of the canal lock, claimed by Holland and Italy, in both of which countries it is believed to have been in use before it was introduced into Britain. The Dutch, at an early period, used what is termed the “bag and spoon” dredger for cleansing their canals. The “spoon” consisted of a ring of iron about 2 ft. in diameter flattened and steeled for about a third of its circumference and having a bag of strong leather attached to it by leathern thongs. The ring and bag were fixed to a pole which was lowered to the bottom from the side of a barge moored in the canal or river. The “spoon” was then dragged along the bottom by a rope made fast to the iron ring actuated by a windlass placed at the other end of the barge, the pole being prevented from rising by a hitched rope which caused the “spoon” to penetrate the bottom and fill the bag. When the “spoon” reached the end of the barge where the windlass was placed, the winding was still continued, and the suspended rope being nearly perpendicular the “bag” was raised to the gunwale of the barge and the excavated material emptied into the barge. The “bag” was then hauled back to the opposite end to be lowered for another supply. This system is still in use, but is only adaptable to a limited depth of water and a soft bottom; it has been largely used in canals and frequently in the Thames. At the Fosdyke Canal in Lincolnshire 135,000 tons were raised in the manner described. According