REDUCTIO AD ABSURDUM. 



REEFS, OR CORAL REEFS. 



Marshal Soult was reduced to defensive operations in the south of 

 France, in 1813 and 1814, he strongly entrenched the heights on all 

 the frontier between the sea about Bayonne and St. Jean-de-Luz, and 

 the mountains at St. Jean-Pied-de-Port ; an extent of above sixteen 

 miles. The works, which were executed in three months, were gene- 

 rally irregular polygons ; and some of them were constructed for 500 

 men. More than a year was spent in raising the redouts which 

 covered Lisbon ; and consequently these were not only strong, but 

 numerous beyond any other example. [ENCAMPMENT.] They were of 

 every trace, but mostly irregular polygons, whose sides sometimes 

 formed re-entering angles, as the ground required : the two great 

 redouts before mentioned were retrenched by interior parapets, which 

 also served as traverses, and each salient point of the redout at Torres 

 Vedras constituted an independent post. 



Attari- and Defence of a Redout. In the attack of a small redout 

 unprovided with artillery, light infantry, or riflemen, keeping for a 

 time as much as possible covered by the inequalities of the ground, 

 endeavour to surround the work, and, by a fire of musketry, directed 

 towards the crest of the parapet, to diminish that of the defenders. 

 The assailing troops then gradually close in upon the redout, and, 

 while one division remains on the counterscarp to continue the fire, 

 should the defenders show themselves upon the parapets, the rest 

 descend into the ditch, where, having collected themselves in parties 

 or small columns, they mount the parapet on each side of a salient 

 angle ; then developing themselves on the summit, they make a general 

 discharge and enter the work. In order to avoid accidents in descend- 

 ing into the ditch, or in ascending the escarp, it is recommended that 

 the bayonets should not be fixed by the assailants till they have gained 

 the benne of the work. 



But if the redout is of considerable magnitude, if it is furnished 

 with artillery, and moreover protected by palisades in the ditches, and 

 abatis or other obstacles in the front, the attack must be conducted 

 with more powerful means. It should commence by a fire of artillery 

 directed partly go as to enfilade the parapets, break down the palisades 

 and derange the abatis, and partly to destroy the merlons which cover 

 the artillery of the work. The fire of the latter being thus in some 

 measure silenced, the light infantry, as in the former case, endeavour 

 by musketry to prevent the defenders from manning the parapets ; 

 and in the "mean time columns of troops advance towards the angles, 

 being preceded by parties of sappers and miners, who make openings 

 for them in the line of abatis, or cover with timbers the trous de loup, 

 if such there be. If the ditch is deep, the descent into it, and the 

 subsequent ascent of the escarp, must be facilitated either by placing 

 scaling-ladders or by throwing in fascines or bags of hay; and any 

 palisades or other obstacles which may not have been displaced by the 

 artillery, must now be cleared away by the working parties which 

 accompany the troops. The fire of the covering parties must cease 

 while the assailants are mounting the parapet, but it must recommence 

 if they should be repelled : in the latter case the storming troops 

 reform their order in the ditch, and again attempt to enter the work. 

 It may be supposed that at length they will succeed, when the de- 

 fenders, if not provided with a redout, to which they may retire for 

 the purpose of capitulating, must surrender at discretion. In 1793, 

 French camp under Valenciennes was protected by works which, 

 I with artillery, were open at the gorge ; and in an 

 attack, the British cavalry, having entered those works at their rear, 



i 'risoners of all the defenders. 



When a redout is threatened with an attack, the officer command- 

 ing it endeavours to provide against the event by disposing in front of 

 the work all possible obstacles to the advance of the enemy, and by 

 placing sand-hags on the parapets in order to cover the defenders, who 

 are to fire through small intervals left for the purpose : these measures 

 should be taken, if not before, during the night preceding the attack ; 

 since the latter generally takes place early in the morning. On the 

 advance of the assailants, the artillery of the work is made to play 

 upon their columns ; and the fire of musketry commences as soon as 

 the latter are within the proper range. These fires are kept up vigo- 

 rously while the assailants are clearing away the obstacles, and until 

 they have descended into the ditch. Should the work have flanks, and 

 the guns behind them be not dismounted, a fire of grape-shot and of 

 niu-ketry must now be directed along the ditches ; while hand-grenades 

 and stones are thrown, and live shells are rolled into them from the 

 jpanpeta of the faces. The storming troops may however persevere, 

 and may at length mount upon the parapet, in which case they must 

 be received by a fire of musketry from the defenders on the terreplein ; 

 and the latter, if overpowered, must endeavour to retire or capitulate. 



Any work* constructed within others, in order to prolong their 

 defence, or to afford a retreat for the troops who occupy them, are also 

 called redouts ; but by the French engineers, reduite or retrench- 

 ments. [RETRENCHMENT; BLOCK-HOUSE.] 



DU'CTIO AD ABSURDUM. [ABSTJBDDU, REDUCTIO AD.] 

 REDUCTION. This term is used in arithmetic in the well-known 

 MOM of the operation of turning one denomination of weights or 

 measures into another : thus shillings may be reduced to pounds, or 

 pounds to shillings. It in also used in the same sense throughout 

 analysis, namely, that of bringing one form into another, making one 

 question depend upon another, Ac. ; in fact, for transformation gene 

 rally. It were to be wished that the latter word transformation ehouk 



e its place whenever the two forms are of equal difficulty or the 

 ;wo questions of the same character, &c., and that reduction should be 

 employed only when there is really a reduction ; that is, a bringing 

 down either of dimension or difficulty, &c. Many writers do use the 

 vord thus, and thus only, but others do not. 



REDUCTION INTO POSSESSION. [POSSESSION.] 



REEFS, or CORAL REEFS, are a peculiar kind of rock which 

 occurs abundantly in some parts of the ocean. They differ from other 

 rocks in extending over a considerable space of the sea in length, with 

 a very narrow width. Generally they are also only a few feet below 

 water ; so that on the side where they are washed by the open sea, a 

 leavy surf is continually running against them. 



Reefs appear under various forms. In some places they are con- 

 ;iguous to the shores, as in the Red Sea ; in others they fringe the 

 shores, being separated from them by a narrow channel of moderate 

 depth. Sometimes they surround islands at a considerable distance 

 from the shores, and the islands so encircled are almost without excep- 

 tion of volcanic origin. Very frequently they surround a portion of 

 the sea, within which there are some small islands, which are often 

 :outiguous to the reefs, and seem to be a part of them, as both are 

 ;omposed of the same material. There are also coral reefs at a great 

 distance from the land, which run nearly parallel to it, like a barrier. 

 Among the latter are those of the Coral Sea, along the eastern coast of 

 Australia. 



The attention of navigators and naturalists was first attracted to 

 those islands which go under the name of Lagoon Islands. A reef 

 approaching in form to a circle surrounds a part of the sea and forms 

 a lagoon, on the inner part of which there are usually several smaller 

 islands, wooded and inhabited, which are contiguous to the reefs them- 

 selves, and frequently extend along them with little interruption. 

 The water on the outside is always nearly unfathomable, but within 

 the reefs good anchorage is generally found, and the reefs themselves 

 have one or more openings of deep water by which the largest vessels 

 may enter the lagoon. Accurate observers soon discovered that the 

 reefs were composed of coral, and were the production of an animal. 

 On these circumstances the first theory of reefs was founded. This 

 theory received some addition from Forster, who accompanied Captain 

 Cook on his second voyage. According to him, they are raised by 

 these small animals perpendicularly like a wall, from a great depth to 

 a very small distance from the surface of the sea. The waves after- 

 wards bring sand, muscles, tang, and pieces of coral, and deposit them 

 on the reef, which, in this way, is gradually raised above the sea-level, 

 and becomes fit for vegetation. Currents and sea-fowls bring the seeds 

 of marine plants, which, being decomposed, form a mould on which 

 the cocoa-nut palm, when carried thither by the waves, thrives luxuri- 

 antly. This theory of Forster was adopted and extended by Flinders, 

 who in surveying the coasts of Australia had abundant opportunities 

 of observing the formation of these islands ; and still more by Peron 

 and Chamisso. The last-mentioned naturalist accompanied Kotzebue 

 on his first voyage of discovery (1815-1818). 



But facts have since been observed by Quoy and Gaimard, who ac- 

 companied Freycinet on his voyage, and published their observations 

 in ^the * Annales des Sciences Naturelles,' which are inconsistent with 

 this theory. They found that the reefs did not entirely consist of 

 coral, and that the layer of coral hardly exceeded a few fathoms in 

 depth. Besides this the polypiaria which are able to form such a layer 

 do not inhabit the sea to any great depth, and are not found where 

 the water is more than 30 feet deep. They therefore supposed that 

 these animals executed their work only iu those parts of the sea 

 where the bottom had been raised by some natural cause nearly to 

 the surface of the water. They supported their theory by adducing 

 the fact that the continuity of every lagoon-reef was broken at one or 

 more places, so as to constitute a strait of very deep water, which 

 could not be the case if these works were carried on at a depth of from 

 100 to 200 fathoms. This theory coincides with the views adopted 

 by Von Buch, in his description of the Canary Islands, and has been 

 adopted by Ehrenberg, in his pamphlet ' Ueber die Natur und Bil- 

 dung der Coralleninsem und Corallenbiinke im rothen Meere ; ' and by 

 Darwin, in the third volume of the ' Surveying Voyages of the Adven- 

 ture and Beagle.' The last-mentioned writer however does not doubt 

 that the reefs which form the lagoon islands are composed of coral to 

 a great depth, much greater indeed than those polypiaria which form 

 them can live in. He explains this in a very ingenious way, by 

 supposing that they formerly had an elevated island in the middle, but 

 that iu those portions of the sea where they now occur, the bottom of 

 the waters was gradually lowered by subsidence, by which the polypiaria 

 were enabled to continue their work farther, and the mountainous 

 islands in the middle disappeared. In other parts of the Pacific and 

 Indian oceans the contrary is supposed to have taken place : the bottom 

 of the sea was elevated, and in these tracts volcanic islands occur. He 

 observes that in this respect these seas may be divided into broad 

 bands, in which an elevation and submersion has alternately taken 

 place ; and he draws from it some important inferences (p. 562-569). 



Mr. Darwin has subsequently produced a work, entitled ' The 

 Structure and Distribution of Coral-Reefs, being the first part of the 

 Geology of the Voyage of the Beagle,' London, 1842, 8vo, pp. 214, in 

 which "he has stated his views in a systematic and comprehensive 

 manner. He observes that, without any distinct intention to classify 



