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the effect is produced. Thus it is noticeable that phers and others, as well as Kant, had attempted while the former or more complete definition replies to Hume, contending that cansality is an corresponds with that expressly given in J. S. intuitive judgment antecedent to experience. But Mill'. Logir, his inductive methods are entirely such a reply remains an arbitrary assertion until it devoted to explaining modes of discovering causes is shown how the causal judgment is connected in the narrower or popular signification.
with experience. In Kant's Critique of Pure It is in this meaning of the term that science Reason this connection is thoroughly investigated; investigates causes. In doing so, it goes on the the refutation of Hume is only part or consequence presupposition that every event or change has a of a complete inquiry into the relation of reason cause. This has been called the Law of Uni. | to experience. It was, however, largely Hume's versal Causation, and may be expressed by doctrine of causality that led to Kant's new point saying that the explanation of every event is of view, and to the doctrine that experience is the to be found in antecedent conditions. Scientific product of the understanding, the realisation of its investigation also presupposes the Law of the a priori forms. It is not the sequence of events in l'niformity of Nature, that the same conditions time, Kant holds, that gives rise to the principle of or canse will be followed (at all times and places) causality ; but the pure notion of cansality finds by the same effects. The grounds and mutual its realisation in this time-sequence, in which each relation of these two assumptions form the chief event is determined by its antecedent. Kant's mbjeet of controversy in the philosophical theory .doctrine, as thus stated, is in full harmony with of causality. It is to Hume that the credit is due the principles and methods of modern science ; of having drawn attention to the difficulties in asserting the principle that every change-i.e. each volred in the principle of causation, in such a way successive state-of the universe is the result of its as to determine the whole course of subsequent preceding state, and at the same time leaving to philosophy. All reasoning about matters of fact, empirical investigation the connection in experi. be abows-all physical science, therefore-depends ence of any one definite thing with any other." on the relation between cause and effect. Yet, The most important discussions of causality are between the cause and the effect there is no dis | those of Hume, Treatise of Human Nature, book i. owerable connection. There appears not, through part iii., and Essay of the Idea of Necessary al nature, any one instance of connection which is Connection ; Kant, Critique of Pure Reason ; and munceivable by us. All events seem entirely loose J. S. Mill, System of Logic, book iii. chaps. iii. -v. and separate. One event follows another ; but we There is also elaborate treatment of the subject in never can observe any tie between them. They the works of Reid, Stewart, and Hamilton. Dr keem conjoined, but never connected.' Hume's own Thomas Brown's Inquiry into the Relation of solutaon of the difficulty is found in the law of Cause and Effect contains much acute analytical pental association. The mind,' he says, 'is thinking. turried by habit upon the appearance of one event Cause Célebre, a convenient French term for to expect its usual attendant, and to believe that a specially interesting and important legal trial, is will exist. This connection, therefore, which we criminal or civil, such as the Douglas Cause fed in the mind, or customary transition of the (1769-71), the Dred Scott case in the United imagination from one object to its usual attendant, States as to the possession of a negro (1856), the is the sentiment or impression from which we form Tichborne case (1871-74). There is a great French the idea of power or necessary connection. Nothing collection of Causes Célebres et interessantes ( 22 vols. further is in the case. ... When we say, there. 1737-45), by Gayot de Pitaval, with modern confore, that one object is connected with another, we tinuations. "See TRIALS. thean only that they have acquired a connection in our thoughts, and give rise to this inference by
Causerie, a name applied to a somewhat short whieh they became proofs of one another's exist
and informal essay on any subject in a newspaper
or magazine. More familiar in manner and slighter ence: a conclusion which is somewhat extraartibary, but which seems founded on sufficient
in structure than the formal essay as usually underendence. The conclusion to which Hume is
stood, it is an excellent medium for a writer whose driven is thus that, while all reasoning about
personality interests the reader as much as the matter of fact is founded on the principle of
value of his thoughts. The name owes its literary casality, this principle has itself no other basis
currency mainly to the famous Causeries du Lundi thuun the mental tendency to pass from one impres.
of Sainte-Beuve ; hardly less valuable examples bon to the idea of another impression previously
were many of the occasional essays in the later experienced in conjunction with the former.
| manner of Matthew Arnold. Hame's solution is thus not sceptical (except as
Caustic (Gr., burning'), in Medicine and in regards the application of causality or any other ! Chemistry, is the term applied to such substances perinciple beyond experience), but it is subjective: as exert a corroding or disintegrating action on the the connection of things is resolved into a customary skin and flesh. Lunar caustic (so called because Opension of ideas. Of the numerous theories of silver was called luna, 'the moon,' in the alchemists' cansation put forward since the question was thus mystical jargon) is nitrate of silver, and common e d, the two most important are J. S. Mill's caustic is potash. When used as a caustic in medi. rehabihtation of Hume's doctrine to suit the re. , cine, the substance is fused and cast into moulds, qurements of scientific investigation, and the which yield the canstic in small sticks the thick. oped doetrine of Kant and his philosopbical ness of an ordinary lead pencil, or rather less.
Caustic is also used in chemistry in an adjective It is characteristic of Mill's doctrine that the sense thus caustic lime, or pure lime, (al, as principle of causality is made a consequence of the distinguished from mild lime, or the carbonate of Law of the Uniformity of Nature : the familiar lime, (acos, caustic magnesia, MgO, and mild truth that invariability of succession is found by 1 magnesia, MgCO3, caustic potash, caustic soda (for okservation to obtain between every fact in nature : these, see POTASH, SODA, &c.). See Cal'TERY. and some other fact which has preceded it.' This Caustics. When the incident rays are parallel frisciple, which is assumed in every scientific in to the principal axis of a reflecting concave mirror, daction, is itself held to be the generalisation of a they converge, after reflection, to a single point, Wade and uncontradicted experience.
called the principal focus. In the case of parabolic A different position is given to the causal prin- ' mirrors this is rigorously true. For, as is easily ciple in Kant's philosophy. The Scottish philoso- , seen from the fundamental property of the para
bola, any ray falling on the mirror parallel to the made of hollow platinum, so arranged that a flame axis is reflected so as to pass exactly through the of benzole can be kept burning in its interior. The focus. For other mirrors it is approximately true galvano-cautery consists essentially of a platinum only when the breadth of the mirror is very small wire which can be heated to any required degree in comparison with its radius of curvature. When by passing a strong galvanic current through it. the breadth of the mirror is large in comparison The cautery is used for three main purposes in with its radius of curvature there is no definite surgery : to produce counter-irritation over an inimage, even of a luminous point. In such cases flamed part (see BLISTER) (actual cautery); to the image is spread over what is called a Caustic, check bleeding (actual or thermo-cautery), by or sometimes a Catacaustic.
slowly destroying the tissues at the bleeding point An example of the caustic is given in the annexed or surface; to perform operations, where the tissues figure for the simplest case-namely, that of rays to be divided are either very vascular (thermofalling directly on a concave spherical mirror, BAB', cautery), or very difficult of access (galvanofrom a point so distant as to be practically parallel. cautery). See CACSTIC.
Two very near rays, Caution, in the Law of Scotland, like Guaranty
as if he were a joint obligant, without suing The curve BCFB' varies of course with the form of the primary debtor, unless the cautioner has the reflecting surface. In the case under considera expressly stipulated that this shall be done. tion it is known as an epicycloid.
The creditor, however, is in every case bound to The reader may see a catacaustic on the surface
use proper precaution in retaining and making of tea in a tea-cup half full by holding the circular available securities. He is not, however, bound rim to the sun's light. The space within the caustic to make the same full disclosure of material curve is all brighter than that without, as it clearly
facts as in insurance, and therefore a cautioner should be, as all the light reflected aflects that should make careful inquiry for himself. Cautionspace, while no point without the curve is affected
ary obligations are generally gratuitous, being, by more than the light reflected from half of the for the most part, undertaken from motives of surface. The rainbow, it may be mentioned, forms friendship; but it is by no means uncommon for one of the most interesting of the whole family of them to be entered into in consideration of a caustics.
premium paid by the person guaranteed, or by When a caustic is produced by refraction, it is those interested in his fortunes. Where a presometimes called a Diacaustic. No such simple mium is paid, the transaction becomes a mere example can be given of the diacaustic curve as insurance of solvency, honesty, or efficiency; and that above given of the catacaustic. It is only in associations of great public utility (see GUARAN. the simplest cases that the curve takes a recognis. TEE) have been formed, both in England and able form. In the case of refraction at a plane Scotland, for the purpose of undertaking to surface, it can be shown that the diacaustic curve guarantee the fidelity of persons employed either is the evolute either of the hyperbola or ellipse, in public or private offices of trust. The tendency according as the refractive index of the medium is of judicial decisions, both in England and Scotland, greater or less than unity,
for many years past, has been to require greater Cauterets, a fashionable French watering:
strictness than formerly in the constitution of place in the department of Hautes-Pyrénées, lies
cautionary obligations ; and under the statutes 3250 feet above sea-level, in the valley of the
| already mentioned all such engagements must be Laverdan, 5 miles S. of Pierrefitte, the nearest
in writing, subscribed by the person undertaking railway station, and 42 SSE. of Pan. The or making them, or by some person duly authorised
by him, otherwise they shall have no effect. If a stationary population was (1886) only 1468, but it is annually swelled in summer by 15,000 to
cautionary obligation is dependent on a condition, 20,000 visitors, for whose accommodation numer.
, it will, of course, be ineffectual unless the condi. ous sumptuous hotels and bathing-establishments
tion be complied with. The cautioner may, in have been built. It is a good centre and guide. !
general, plead every defence which was competent station for ascents among the Pyrenees. The
to the principal debtor, and the extinction of the sulphurous springs, twenty-five in number, and
primary obligation extinguishes the secondary one. varying in temperature from 60° to 131° F., are
The cautioner is discharged by any essential charge the most abundant in the Pyrenees (330,000 gallons
being made on the obligation of the debtor, or in per day), and have been known from Roman
respect of the person relied on, without his assent. times, though their modern reputation dates from
The statute expressly provides that changes of the 16th century, when Margaret, sister of Francis ! partnership either of creditor or debtor will ex. I., held her literary court and wrote much of her | tinguish the guarantee. If the creditor gives time Heptameron at ('auterets.
-e.g. takes bills from the debtor of an unusual
currency--that will also operate discharge. The Cantery (Gr. kaio, I burn'), in Medicine, is discharge of one cautioner, moreover, unless con. used of any substance which burns the tissues. sented to by the rest, is a discharge to all. The (The term 'potential cautery,' as applied to caustie cautioner is entitled, on full payment, though not substances, is becoming obsolete.) The actual on payment by a dividend, to an assignation of the cautery is an instrument with a head or blade of debt and diligence, by which means he comes, in steel, iron, or platinum, which is heated in a fire or all respects, into the creditor's place; and morespirit-lamp. In the thermo-rautery (or Paquelin's lover, if the solvency or other conditions of the cautery, from its inventor), the head or blade is ' principal debtor should seem precarious, he may
dopt legal measures for his relief. Co-cautioners, to his generalship. His task being done, he or persons bound together, whether their obliga-resigned his power into the hands of the National to be embodied in one or several deeds, are Assembly, which appointed him President of the entitled to mutual relief. But where a co-cautioner Council. As a candidate for the presidency of the obtains relief from the others, he must communicate republic, when Louis Napoleon was elected, he to them the benefit of any deduction or ease which received nearly a million and a half of votes out may have been allowed him in paying the debt. of 7,327,345. On the coup d'état of December 1851,
Letter of credit and recommendation raise much Cavaignac was arrested, but released after a short the same relation of parties as a formal cautionary detention ; and though he consistently refused to obligation, but since 1856 a mere verbal introduc. give in his adhesion to the Empire, he was per
cannot have that effect. For the forms andmitted to reside in France without molestation. ctfects of ordinary mercantile guarantees, and for He died, 28th October 1857, at his country house the forms of guarantee insurance of fidelity, see near Tours. Cavaignac was an able soldier, a GIARANTEE. For the Scottish cautionary obliga zealous republican, and in every way an honour. tion in cash-credit bond, see BANKING, II. 713. able man. See his Life by Deschamps (2 vols. JI'
D IAL CAUTIOx, in the Law of Scotland, is Paris, 1870). od two kinds—for appearance, and for payment. If
Cavaillon (ancient Cabellio), a town of the * creditor makes oath before a magistrate, that he French department of Vaucluse. 18 miles SE. of believes his debtor to be meditating flight (in medi. Avignon by rail, with a cathedral, and some tation fuga ), he may obtain a warrant for his
Roman remains. Pop. 5164.
Romani a prebension; and should he succeed in proving the alleged intention to flee, he may compel him
Cavalcanti, Guido, Italian poet, born in 1230, to find cantion to abide the judgment of a court
was banished, for mercantile transactions with a jadro sisti). The cautioner, or surety, under:
Guelph, by the Ghibellines, a daughter of one of take that the defender shall appear to answer any
whose chiefs he had married, and returned in wtion that may be brought within six months.
broken health to Florence only to die there, about The old Bond of Presentation, by which in order to
1300. His works -sonnets, ballads, and canzoni
are remarkable alike from their language and depth pun time the surety undertook to produce the debeor or pay the debt at a future date, is now
of thought, although his epicurean philosophy supersedel by the abolition of imprisonment for
gained him, among his contemporaries, the reputadebe There is also a form of judicial caution
Ition of an atheist. See Ercole, Guido Cavalcanti called judicatum solri, given in cases of general
e le sue Rime (Milan, 1885).-Another of the name, Inning of arrestment of ships, in which the surety i
BARTOLOMMEO (1503-62), a noble and eloquent becaines liable for the whole debt. The commonest
| Florentine, led a revolt against the Medici, and form of judicial caution, however, is the security
| was afterwards employed by Pope Paul III. cally given in the Bill Chamber (q.v.), when a bill Cavalcaselle, GIOVANNI BATTISTA, Italian verbond is brought under suspension : the security is art writer, born 22d January 1820, at Legnago, for the principal sum and expenses, if the suspen. early visited the art centres of Italy, and in 1846 eing should be refused. Interdict is also frequently proceeded to Germany, where he met J. A. Crowe granted upon caution for the damages that may i (q.v.), with whom he returned to Italy. Banished result from the interdict, should it turn out to have for his share in the revolution of 1848, he accom. been wrongly obtained.
i panied ('rowe to London, and there their first joint Cauvery. See KAVERI.
work, Early Flemish Painters (1857; 3d ed. 1879), Cava del Tirreni, a town of Italy, in a lovely
was published. Cavalcaselle returned to Italy in
1858, and in 1861 commenced with Crowe the History Talley, 51 miles NW. of Salerno by rail, with a cathedral, and manufactures of silk, woollens,
i of Painting in Italy (Lond. 5 vols. 1864-71). Other
joint works are Titian (1876) and Raphael (1883); cotton, and linen. Pop. 6339. About a mile distant in the Benedictine monastery of the Trinity,
Cavalcaselle's independent writings are of less
importance. He is head of the art department in celebrated for its archives.
the ministry of Public Instruction at Rome. Cavagnari, Sir Louis, born in France in 1841, was educated at Christ's Hospital, London, and in
Cavalier (Fr., from Lat. caballus, 'a nag'), 1657 was naturalised as a British subject. He had "
from “horseman ' acquired the meaning of knight' seen twenty-one years' military and political service
or 'gallant,' in which sense it is used by Shake. in India, when on 3d September 1879 he was
speare (Henry V., III. 24), like caralero, in Henry
. Part v. ii. 62. In 1641 · Cavaliers' was murdered at Kabul. See AFGHANISTAN.
applied as a nickname to Charles's partisans in Caraignac, Louis ErGÈNE, born in Paris, 15th opposition to the Roundheads, or friends of the (Actober 1902, was a son of General Jean Baptiste Parliament; and from a term of reproach it came ('araignac (1762-1829), a member of the National to be adopted as a title of honour, until, after 1679, ('ouvention. Educated for the military profession, it was superseded by Tory. For the Cavalier be first served in the Morea, and afterwards in Parliament' (1661-79), see CHARLES II. Airia, whither he was sent in 1832 into a kind of bunourable exile, in consequence of a too free ex.
| Cavalier, JEAN, a journeyman baker, from pression of opinion in favour of republican institu
* Ribaute, near Anduze, who, born in 168), in 1702 tin Here he won great distinction by his energy,
became a famous leader of the Camisards (9.v.), toolbens, and intrepidity, was made chef de bataillon
withal a prophet and preacher. He surrendered in 1937, and rose to the rank of brigade-general in
to Villars in 1704, and entered the service of 1944. In 1848 he was appointed governor-general
Savoy ; but in 1711 we find him settled with a of Algeria, but in view of the impending revolu.
British pension in England, and he died at Chelsea, tionary dangers, was called to Paris and assumed
governor of Jersey, 17th May 1740. See a long the office of Minister of War. He was appointed
article in vol. ix. of the Inet. of National Biomilitary dictator in order to suppress the formid. i
graphy (1887). able insurrection of June, which he quelled only ! Cavaliere Servente. See CicIsBEO. after & most obstinate contest continued from Cavalry is a general name for horse-soldiers or the 234 to the 26th June. It is estimated that a troopers trained to act in a body. In the British greater number of Frenchmen fell in the struggle army there are 31 regiments of European, and 30 of than in the bloodliest battles of the first Empire. native Indian cavalry. The former comprise 2 Caraigan's clemency to the vanquished was equal regiments of Life Guards (red), 1 of Horse Guards 32
(blue), and 7 of Dragoon Guards, classified as heavy in front, and the 'serrefiles,' or supernumerary noncavalry ; 3 regiments of Dragoons, and 5 of Lancers, commissioned officers, in rear. There is an interval classified as medium ; and 13 Hussar regiments or of 12 yards between squadrons. The pace is, walk light cavalry-all carrying carbines and swords. 4 miles an hour, trot 8, gallop 12. The maximum The war strength of each is 1 lieutenant-colonel, distance covered by cavalry is 68 miles by day I major, 8 captains, 9 lieutenants, 7 sub-lieutenants, / (6 A.M. to 10 P.M.) and 18 by night-86 for the I adjutant, 1 paymaster, 1 quartermaster, 1 medical 24 hours ; but after such a march there must be a officer, 1 veterinary surgeon, 75 non-commissioned rest all next day. For a continuous march 35 officers, 8 farriers, 8 shoeing-smiths, 8 trumpeters, miles a day, at 5 miles an hour, is a good rate. 4 saddlers, 2 wheelers, 15 bandsmen, 480 troopers, Duties on Service.-In large armies, from oneand 22 drivers, 559 riding and 44 draught horses, eighth to one quarter of the whole force should be and 11 wagons.
cavalry. Their duties are to cover the movements The native Indian cavalry are all light, and some of their own army, and to find out those of the have the front ranks arined with lances, the rear enemy-besides taking part in the actual battles by with sabres. Bengal has 19 regiments, each of 8 guarding the flanks, seizing all opportunities of troops, consisting of 10 European officers (1 in com. charging, completing success by an active pursuit, mand and I surgeon), 17 native officers, and 536 or covering defeat. The screening and reconnoitring native non-commissioned officers and troopers. duties are performed by the cavalry divisions, each Madras has 4 regiments of only 6 troops each, the of two or more brigades, one or two days' march in same number of European, but 12 native officers front of the main body. The light Brigades (q.v.) and 396 of other ranks. Bombay has 7 regiments are perhaps best for the actual scouting, but must with the same organisation and numbers as Bengal, be supported by heavy cavalry in order to meet that but only 518 native non-commissioned officers and of the enemy, which would otherwise have the troopers. Besides these regiments there is a troopadvantage of greater weight in the charge. Each of native cavalry at Aden, and one as a body-guard brigade of two or more regiments is accompanied for each lieutenant-governor, and the governor. by a battery of Horse Artillery. general of India.
The battle of Mars la Tour in the Franco-German The auxiliary cavalry in Great Britain comprises war of 1870, supplies the best examples of a cavalry 39 regiments of Yeomanry, 2 of Volunteer Light fight on a large scale, and of a charge (that of Horse, and I of Volunteer Mounted Rifles, of various Barby and Bredows' brigades) directed against in. strengths. There is a cavalry depôt at Canterbury, fantry. The action of the German cavalry through. and a school of instruction for auxiliary cavalry at out the same campaign illustrates the screening and Aldershot.
reconnoitring duties of the arm. The capture of After the American civil war, the United Cairo by the rapid advance of the British cavalry States' cavalry was reduced to 10 regiments of after the battle of Tel-el-Kebir (1882), shows its 936 privates each. The commissioned officers of value after a successful engagement. a regiment consist of 1 colonel, 1 lieutenant- Tactics.-Unless acting dismounted, cavalry must colonel, 3 majors, 12 captains, 14 first lieutenants, either attack or retire; it cannot otherwise defend and 12 second lieutenants.
itself. Against cavalry it must therefore manœuvre History.-For the place of cavalry in the ancient with its first line, so as to attack to the best advan. armies, see ARMY. In the middle ages horsemen tage-i.e. against the adversary's flank. Its second -knights, esquires, and their attendants-formed line following, en échelon, in order to have a clear the most important part of the great armies ; but front, protects the flanks of the first from counter after the disappearance of the Roman cohort with attack, and supports its movement, completing its its 132 highly trained horsemen, the organisation victory, or covering its retreat. Horse artillery of cavalry, as we now understand the word, was on the protected flank fire upon the enemy up to the neglected until 1445, when Charles VII. of France last moment before the charge. A third portion, grouped his men-at-arms into companies 100 strong. formed into a reserve, follows, and behind it the The method of fighting, from 1645 until Frederick other two can rally after the charge, which, even the Great introduced the charge or shock tactics, when successful, creates great confusion, Cavalry was to advance to close quarters, fire pistols from attacks 'artillery in two bodies--one in line formathe saddle, and then commence cutting with the tion charges the escort, and the other in extended sword. The value of dismounted cavalry able to order, the men a horse's length apart, converges act as infantry was then recognised, and dragoons upon the guns. Infantry can defend itself from a armed with muskets were much in vogue until the cavalry charge, unless surprised by a flank attack, beginning of the 19th century. They then lost which would generally be delivered by comparafavour, and though all European nations continued tively small bodies in successive lines, but such an to train their troopers to dismount and use their opportunity rarely occurs on a modern battlefield. carbines to hold some important point until the Cav'an, an inland county in the south of Ulster. arrival of infantry, it was taught that the sword | It lies in the narrowest part of Ireland, 18 miles was their proper weapon, and the saddle their from the Atlantic, and 20 from the Irish Sea Area, proper place. But Russia has lately armed all her
| 746 sq. m., of which less than a third is under crops. cavalry, except the Cossacks, with long rifles, thus
Bogs and hills, with many small lakes, are found in turning them into dragoons, and it is now generally the north-west, where Cuicagh attains a maximum felt that the dismounted service of cavalry must be altitude of 2188 feet. The chief rivers are the Erne, developed to a greater extent than has hitherto the Woodford, and the Annalee. The eastern half of been the case. Mounted infantry too, using their
Cavan rests on clay-slate and graywacke; the moun. horses merely as a means of rapidly covering the tain district in the west is carboniferous formation. ground, have been found so useful in the British
Of minerals, Cavan affords coal, iron, lead, and army, that in 1887 a school for this arm was formed
copper, with many mineral springs. The climate is at Aldershot; and it has been decided that a force
cold and damp; and the soil is poor, wet, and 900 strong shall accompany the cavalry division on clayey, except along the streams. The chief crops active service.
are oats and potatoes, the cultivation of flax having Formation.--A cavalry regiment in the field is
greatly decreased since 1830. The farms are small. divided into 4 squadrons, each of 2 troops. The
Agriculture forms the staple industry, but linen is men of each squadron when in line are 6 inches
manufactured to a considerable extent. The chief from knee to knee, and formed in two ranks, a horse's
| towns are Cavan, Cootehill, and Belty** Cavan length apart. The officers are at a similar distance returns two members to parliament
174,064; (1881) 129,176, of whom 104,328 were these are simply great blisters or hollows formed Catholics, and 18,990 Episcopalians.-CAVAN, the by the expansive power of the highly heated county town, stands on a branch of the Annalee, vapours contained in the lava at the time of its $S miles YW. of Dublin by rail. It has a court eruption. Others again may have been caused by house and a grammar-school; and the beautiful the sudden conversion into steam of the water of demesse of Lord Farnham lies between Cavan and lakes or streams suddenly overwhelmed by a lavaLough Oughter, which is about 5 miles west. Pop. flow-the steam thus generated might either isl, 3030.
violently rupture the lava by its explosive force, or Cavati'na, a short form of operatic air, of a
produce great tunnels and irregular cavities under 1 month and melodious character, differing from the
the liquid lava, already inclosed in its solid crust, ordinary aria in consisting only of one part, and
by pressing it upwards. The extensive Fossa i frequently appearing as part of a grand scena.
della Palomba of Etna is supposed by some to have Examples of cavatina are found in many well
had such an origin. But probably the greater I know operas, as Sonnambula and Les Huguenots.
number of the larger caves under lava have been The term is also often used for a complete air or
formed by the escape of the lava itself from its own · song, such as the Salve dimora ' in Faust.
solidified envelope. When lava pours out from a
volcanic orifice it very rapidly coagulates above Cave, or CAVERN (Lat. cavus, 'hollow'). The and below, so that the liquid rock becomes imnatural hollows which occur in and underneath prisoned in a hardened crust of its own material. rocks have originated in various ways-some being The great pressure of the inclosed lava, however, due to the chemical and mechanical action of upon the crust at the terminal point of the flow water, others to dislocations and disruptions pro suffices again and again to rupture it, and the lava duced by movements of the crust, or by superficial then flows out freely until it is again imprisoned in rock-falls and landslips, while yet others are tunnels the same manner. In the case of very liquid lavas which now and again occur in or under thick sheets this escape is often completed in a perfect manner of lare Caves formed by marine erosion are fre --and a long underground tunnel is left behind, quently met with along the coast-line of Britain and from the roof of which depend long stalactites of odber countries, Fingal's Cave at Staffa (9.v.) being black glassy lava. Extensive caves formed in this
splendid example. They are not confined to any way-some of them measuring over 100 feet in particular kind of rock-although, other things width-occur in the Azores, the Canary Islands, being equal, they are of course more easily formed Iceland, and other volcanic regions. in readily yielding rocks than in more durable kinds. Another class of caves embraces such hollows It is rather the character of their natural division as have originated during earthquakes or other planes or beds and joints than their composition movements in the crust of the earth. At such and texture that determines whether the rocks at times rocks are rent asunder, and when they fall tbe l e of a sea-cliff shall be hollowed out or not rudely together irregular cavities are left between by the action of the waves. If the rocks are thin the disjointed masses, and similar results often Ledded and abundantly and regularly jointed, it is take place when great landslips occur. But the obrious that as soon as any portion is undermined most extensive caves and underground galleries by the sea, the overlying masses will immediately have been excavated by the chemical and mechan. yield along their division-planes and topple down. | ical action of underground water. Sometimes li, on the other hand, the rocks are meagrely and these hollows continue more or less persistently inregularly jointed, and occur in massive beds, then in one direction, but most usually they wind they will not so readily collapse when undermined, tortuously about, and often open into similar and caves will tend to be formed. Caves which intricate galleries, which, in like manner, com. have had this origin are not uncommonly met with municate with lateral extensions of the same char. along the line of old sea-margins in many regions acter. There can be no doubt that caves of this which have been elevated in recent geological / kind are the channels of underground streams and tirnes. Most frequently, however, the entrances rivers, and that they have been excavated, in the to such caves are concealed by the rock-rubbish first place, by the chemical action of acidulated which has been detached from time to time by the water making its way downwards from the surface action of the weather from the cliffs above. | along the natural division-planes of the rocks, Care of erosion are also formed by river-action until eventually space has been licked out for the at the base of crags and cliffs in many valleys. passage of a subterranean stream. The cavities And now and again such hollows may be detected would then tend to be enlarged by the filing action at various levels in river-cliffs, as if they had been of the sand and gravel which the underground formed during the gradual excavation of the ravines stream and its numerous feeders might sweep in which they occur.
along. Many such underground watercourses are In Britain and other countries long occupied by well known at the present day, and the direction man most of such river-cliff caves or rock-shelters of some of them can be traced by the swallow holes, have been artificially deepened and widened, and chasms, and sinks,' which indicate places where this to such an extent that it is often hard to the roofs of the cavities have given way, or have say how much of the work can be attributed to been pierced by the action of acidulated water. In nature. By far the most important caves, how. certain regions almost all the drainage is thus con. ever, are those which owe their origin to the ducted underground-rivers after Howing for a action of underground water. But before these are considerable distance at the surface suddenly dis. described, mention may be made of the hollows appear, and follow a hidden course, for it may be which occur now and again in and under lava- many miles, before they emerge again to the light for. Where lava has flowed over and solidified of day. Sometimes, indeed, they never come to alume a mass of snow and ice, the subsequent the surface again, but enter the sea by subterranean melting of the latter will leave a hollow behind. channels. Should anything occur (such as earthNear the Casa Inglese, on the south-east side of the quakes, &c.) to interrupt such a system of underhighest cone of Etna, a mass of ice of unknown ground drainage, and the streams and rivers be extent and thickness, covered by lava, was seen compelled into new channels, the old subterranean by Lyell in 1828 and again in 1858. But this, courses will then become galleries more or less dry, I must be remembered, is at a height of 10,000 which may be accessible by one or even by several feet above the sea. In lava itself, however. | openings. savo of considerable extent occur. Many of ! As it cannot be doubted that all such great