So that the declination here seems oscillating about a limit.

According to the observations of Mr. Canton for the year 1759 (Phil. Trans. vol. 51. pa. 445.) it appears that the diurnal variation of declination increased from 7' 8" in January, to 13' 21" in June, and decreased to about 6 58" in December.

Mr. Gilpin found (Phil. Trans. 1806, part ii.) by a mean of 12 years from 1793 to 1805, that the declination appeared to increase or go westward from the winter solstice to the vernal equinox, 080; to diminish or go eastward from the vernal equinox to the summer solstice, 1'43; to increase again from the summer solstice to the autumnal equinox, 243: and to decrease only 0/14 from thence to the winter solstice.

Mr. Thomas Harding, in the Transactions of the Royal Irish Academy, vol. iv. has given observations on the declination of the magnetic needle at Dublin, which are rather extraordinary. He says the change in the declination at that place is uniform. That from the year 1657, in which the declination was nothing (the same as at London in that year), it has been going on at the medium rate of 12/20 annually, and was in May 1791, 27° 23' west: exceeding that at London by 3 or 4 degrees. We know not whether observations subsequent to 1791 favour the same result.

At Paris, according to Orontius Finæus, the declination was, in 1550 8° 0'E. in 1640 in 1660

30Е.
00

2 2 W. 18 10 W.

18 20 W. 21 54 W. 22 15 W.

22 0 W.

21 45 W. 1803 21 59 W. 1804 - 22 15 W.

The declinations during this period appearing obviously to vacillate about a limit.

M. Burckardt, an ingenious French astronomer, invented a formula to represent the magnetic declinations observed at Paris; thus, if t denote the number of years from 1663, the tangent of the declination is 0-449 sin. (25'7") t+0.0425 [sin. (50′13′′) t]+00267 [sin. (1°40/26") t]. It follows from this formula that the eastern declination diminished from 1448, when it was at its maximum of 24° 10', to 1660 or 1663, when it was nothing at Paris. Reckoning an equal period backward from 1448 gave 1233 for the earlier epoch when there was no declination. A little before this the invention of the mariner's compass is ge. nerally dated. According to Burckardt's theorem, the maximum of western declination at Paris will be in the year 1831; though it will not vary more than 20 minutes from that time to 1878. We mention these as curious results of this astronomer's formula; but would by no

means be understood as affirming their ac

curacy.

According to Mr. James Robertson (Phil. Trans. 1806), the magnetic declination at Jamaica has undergone no change since the year 1660, or more than 140 years. Indeed, observations prove abundantly, that the variations of the declination compared with one another in different points of the globe, follow different relations. But there is a fact extremely worthy of attention, that has been remarked by the celebrated Hallé, on the mere inspection of the table of declination published by Van Swinden, whose notice it had escaped. In the table, three places are pointed out, where the needle has experienced the greatest declination: and these are, first, in the middle of the Indian ocean, from 10° to 15° of south latitude, and from 82° to 87 of east longitude (reckoning from the isle of Ferro), where the variation, from the year 1700 to that of 1756, was from 11° to 11° 15'. Secondly, in the Ethiopian ocean, from 5o of north to 20° or 25° of south latitude, and in the interval of 10°, 15°, and 20°, of east longitude; the variation relative to this space, during the same period of time, was from 10° to 10° 45', principally under the line and to 50 southward. Thirdly, at 50° north latitude, and between 17° of east and 10o of west longitude; where again, in the same period, there was a variation of from 11° to 11° 45'.

Looking at Van Swinden's table, Hallé perceived that these three places formed as it were three centres, round which the numbers indicating the quantities of variation insensibly decreased in proportion as we departed from each centre; so that we have here a new order of observations, answering to the places where the variation was least in the same course of years.

These places are, first, the whole American ocean, without including the gulf of Mexico, that is to say, from the western point of Africa to the farthest of the Bermuda islands. And here also we must remark, that in the ocean between Africa and North America, the variation is much less towards the American than towards the African coasts. Secondly, the environs of the isle of Madagascar, and part of the coast of Zanguebar. Thirdly, that part of the ocean which is to the south and south-east of the Sunda islands, between those islands and New Holland. And lastly, in the same sea, about the 4th degree of south latitude and the 97th of east longitude, that is, in the middle of the space comprised between the western angle of New Holland and the southern point of Africa. In all these different places the declination of the needle has not varied, during the whole 56 years, so much as one degree. (Encyclop. Method.)

Dr. Halley published in the last century a theory of the variations of the compass. In this work he supposes there are four magnetic poles in the earth; two of which are fixed and two moveable, by which he explains the dif ferent variation of the compass at different times in the same place. But it is impossible

to apply exact calculations to so complicated an hypothesis. M. Euler, son of the celebrated geometrician of that name, has how. ever shown, that two magnetic poles placed on the surface of the earth will sufficiently account for the singular figure assumed by the lines which pass through all the points of equal variation in the chart of Dr. Halley.

M. Euler first examines the case wherein the two magnetic poles are diametrically opposite; second, he places them in the two opposite meridians, but at unequal distances from the poles of the world; third, he places them in the same meridians. Finally, he considers them situated in two different meridians. These four cases may become equally important; because, if it is determined that there are only two magnetic poles, and that these poles change their situations, it may some time hereafter be discovered that they pass through all the different positions.

Since the needle of the compass ought always to be in the plane which passes through the place of observation and two magnetic poles, the problem is reduced to the discovery of the angle contained between this plane and the plane of the meridian. M. Euler, after having examined the different cases, finds that they also express the earth's magnetism, represented in the chart published by Messrs. Mountaine and Dodson in 1774, particularly throughout Europe and North America, if the following principles are established.

Between the arctic pole and the magnetic pole 14° 53'.

Between the antarctic pole and the other magnetic pole 29° 23′.

53° 18' the angle at the north pole, formed by the meridian's passing through the two magnetic poles.

250° the longitude of the meridian, which passes over the northern magnetic pole.

As the observations which have been collected with regard to the variation are for the most part loose and inaccurate, it is impossible to represent them all with precision; and the great variations observed in the Indian ocean seem to require, says M. Euler, that the three first quantities should be 14, 35, and 65 degrees.

In the Memoir of MM. Biot and Humboldt "On the variations of the terrestrial magnetism in different latitudes," the position of the magnetic equator is determined from direct observations. The inclination of the plane of this circle to the astronomical equator is stated to be 10° 58′ 56", its occidental node on that equator being at 120° 2′ 5′′ longitude W. from Paris, the other node at 59° 57′ 55′′ E. of Paris. The points where the axis of the magnetic equator pierces the earth's surface are, the northern point at 79° 1' 4" N. lat. and 30o 2′ 5′′ W. long, from Paris; the south ern point is situated in the same latitude south, and 149° 57′ 55" E. long. from Paris.

It would carry us far beyond our limits were we to attempt to sketch the various theories of terrestrial magnetism which have been pro

posed: we must, therefore, refer to Birch's History of the Royal Society, vol. iii. 131; Halley, in Phil. Trans. No. 148; Cavalla's Magnetism, and Lorimer's Supplement to ditto; Montucla, Histoire des Mathematiques, vol. iv. 510; Gregory's translation of Haüy's Natural Philosophy, vol. ii. 105-130; and Bain on the Variation of the Compass.

DECLINATION OF A VERTICAL PLANE, or WALL, in dialling, is an arch of the horizon, comprehended either between the plane and the prime vertical circle, when it is counted from the east or west; or between the plane and the meridian, if it be accounted from the north or south.

DECLINATOR, or DECLINATORY, an instrument in dialling, by which the declination, inclination, and reclination of planes are determined. The construction of this instrument, as somewhat improved by Mr. Jones, is as follows: on a mahogany board ABIK, fig. 9, Pl. 56, is inserted a semicircular arch AGEB of ivory or box-wood, divided into two quadrants of 90° each, beginning from the middle G. On the centre C turns a vertical quadrant DFE, divided into 90°, beginning from the base E; on which is a moveable index CF, with a small hole at F for the sun's rays to pass through, and form a spot on a mark at C. The lower extremity of the qua drant at E is pointed, to mark the linear direction of the quadrant when applied to any other plane; as this quadrant takes off occasionally, and a plumb-line P hangs at the centre on C, for taking the inclinations and reclinations of planes. At H, on the plane of the board, is inserted a compass of points and degrees, with a magnetical needle turning on a pivot over it. The addition of the moveable quadrant index considerably extends the utility of the declinator, by rendering it convenient for taking equal altitudes of the sun, the sun's altitude, and bearing, at the same time, &c.

To apply this instrument in taking the declination of a wall or plane: place the side ACB in an horizontal direction to the plane proposed, and observe what degree or point of the compass the N part of the needle stands over from the north or the south, and it will be the declination of the plane from the north or south accordingly. In this case, allowance must be made for the variation of the needle (if any) at the place; and which, if not previously known, will render this operation very inaccurate. At London it is now 24 9' to the west.

Another way more exact may be used, when the sun shines out half an hour before noon. The side ACB being placed against the plane, the quadrant must be so moved on the semicircle AGB, and the index CF on DE, till the sun's rays passing through the hole at F fall exactly on the mark at G, and continued so till the sun requires the index to be raised no higher; you will then have the meridian or greatest altitude of the sun; and the angle contained between G and E will be the declination required. The position of CE is the me

ridian or 12 o'clock line.

But the most exact way for taking the declination of a plane, or finding a meridian line, by this instrument, is, in the forenoon, about two or three hours before 12 o'clock, to observe two or three heights or altitudes EF of the sun; and at the same time the respective angular polar distances GE from G write them down; and in the afternoon watch for the same, or one of the same altitudes, and mark the angular distances or distance on the quadrant AG: now, the division or degree exactly between the two noted angular distances will be the true meridian, and the distance at which it may fall from the C of the divisions at G will be the declination of the plane. The reason for observing two or three altitudes and angles in the morning is, that in case there should be clouds in the afternoon, you may have the chance of one corresponding altitude.

The quadrant occasionally takes off at C, in order to place it on the surface of a pedestal or plane intended for an horizontal dial; and thereby from equal altitudes of the sun, as above, draw a meridian or twelve o'clock line to set the dial by.

The base ABIK serves to take the inclination and reclination of planes. In this case, the quadrant is taken off, and the plummet P is fitted on a pin at the centre C: then the side IGK being applied to the plane proposed, as QL (fig. 10.) if the plumb-line cuts the semicircle in the point G, the plane is horizontal; or if it cut the quadrant in any point at S, then will GCS be the angle of inclination. Lastly, if applying the side ACB (fig. 10.) to the plane, the plummet cuts G, the plane is vertical; or if it cuts either of the quadrants, it is accordingly the angle of reclination. Hence, if the quantity of the angle of inclination be compared with the elevation of the pole and equator, it is easily known whether the plane be inclined or reclined.

To DECLINE. v. n. (declino, Lat.) 1. To lean downward (Shakspeare). 2. To deviate; to run into obliquities (Exodus). 3. To shun; to avoid to do any thing. 4. To sink; to be impaired; to decay (Denham).

To DECLINE. v. a. 1. To bend downward; to bring down (Spenser). 2. To shun; to avoid; to refuse (Clarendon). 3. To modify a word by various terminations; to infiect (Watts.).

DECLINE. 8. The state of tendency to the worse; diminution; decay (Prior).

DECLIVITY. s. (declivis, Latin.) Inclination or obliquity reckoned downward; gradual descent; the contrary to acclivity (Swift). DECLI/VOUS. a. (declivis, Latin.) Gradually descending; not precipitous.

T5 DECO CT. v. a. (decoquo, decoctum, Lat.) 1. To prepare by boiling for any use; to digest in hot water (Bacon). 2. To digest by the heat of the stomach (Davies). 3. To boil in water (Bacon). 4. To boil up to a consistence (Shakspeare).

DECOCTIBLE. a. (from decoel.) That may be boiled, or prepared by boiling.

DECO'CTION. s. (decoctum, Lat.) The act of boiling any thing, to extract its virtues (Bacon).

DECOCTION. (decoctum, from decoquo, to boil.) In pharmacy, any medicine boiled in a watery fluid. In a chemical point of view it is a continued ebullition with water, to se parate such parts of bodies as are only soluble at that degree of heat. The following are the chief preparations in modern dispensatories.

D. althææ. This preparation, directed in the Edinburgh Pharmacopoeia, may be exhibited as a common drink in nephralgia, and many diseases of the urinary passages, with advantage.

D. chamameli. A very common and excellent vehicle for tonic powders, pills, &c. It is also in frequent use for fermentation and clysters.

D. cinchonæ. This way of administering the bark is very general, as all the other preparations may be mixed with it as necessity requires. It is a very proper fomentation for prolapsus of the uterus and rectum.

This

D. cornu cervi. Decoctum album. preparation of hartshorn possesses absorbent and antacid qualities, and is a very excellent drink in fevers attended with diarrhoea, and acidities of the prima viæ.

D. Geoffrææ. This is by far the most proper form for administering this medicine, which possesses laxative, narcotic, and anthelmintic virtues.

D. guaiaci compositum. This possesses stimulant and diaphoretic qualities, and is generally exhibited in cutaneous diseases which are dependant on a vitiated state of the humours.

D. hellebori albi. The itch and some erup tions of the scalp are occasionally removed by this application, which should be used as a lotion.

D. hordei. Barley decoction is a very nutritive and softening drink and the most proper of all liquors in inflammatory diseases. It is an excellent gargle in inflammatory sore throats, mixed with a little nitre.

D. hordei compositum. From the pectoral and demulcent qualities of this decoction, it may be administered as a common drink in catarrh, and several affections of the chest.

D. mezerei. An acrid and very stimulating decoction, sometimes exhibited in indolent glandular swellings.

D. pro enemate. A very excellent form for an emollient clyster. A variety of medicines may be added to answer particular indications.

D. pro fomento. This preparation possesses antiseptic properties, and may be directed with advantage in sphacelus.

D. sarsaparillæ. This is much extolled by some practitioners in phthisis, and serves to restore the strength after a long course of mercury.

D. sarsaparillæ compositum. The alterative property of this compound is very great: it is generally given after a course of mercury, where there has been nodes and indolent ulcerations, and with great benefit.

D senekæ. The chief qualities of the se

neka are contained in this form. An addition of a small quantity of liquorice obviates an unpleasant sensation otherwise produced by it in the fauces.

D. ulmi. This may be employed, with great advantage, as a collyriam in chronic ophthalmia. It is given internally in some cutaneous eruptions.

DECOCTURE, 8 (from decoct.) A sub. stance drawn by decoction.

DECOLLATION. 8. (decollatio, Latin.) The act of beheading (Brown).

DECOMPO'SITE. a. (decompositus, Latin.) Compounded a second time (Bacon). DECOMPOSITION, in chemistry, the dis. union of substances already joined together; a change which is uniformly succeeded by the formation of new compounds. Few chemical processes take place without a decomposition of some kind; and hence decompositions are almost innumerable in their variety, and depend upon the nature of the chemical substances employed. See ANALYSIS.

DECOMPOSITION OF FORCES, LELOGRAM OF FORCES.

See PARAL

To DECOMPOUND. v. a. (decompono, Latin.) 1. To compose of things already compounded; to compound a second time (Newton). 2. To resolve a compound into simple parts.

DECOMPOUND. a. (from the verb.) Composed of things or words already compounded; compounded a second time (Boyle).

DECOMPOUND LEAF. In botany, when the primary petiole is so divided that each part forms a compound leaf. The different kinds of the decompound leaf are BIGEMINATE, BITERNATE, and BIPINNATE: which see in their proper places.

DE CORÂMENT. s. (from decorate.) Ornament; embellishment.

To

To DECORATE. v. a. (decoro, Lat.) adorn; to embellish; to beautify. DECORATION. 8. (from decorate.) Or. nament; added beauty (Dryden).

DECORATION, in architecture, any thing that adorns and enriches a building, church, triumphal arch, or the like, either without side, or within. The orders of architecture contribute greatly to decoration; and paint ings, vases, festoons, &c. are often very successfully applied.

DECORATION is more particularly applied to the scenes of theatres. In operas, and other theatrical performances, the decorations must be frequently changed conformably to the subject. The ancients had two kinds of decora. tions for their theatres: the first, called versatiles, having three sides, or faces, which were turned successively to the spectators: the other called ductiles, showing a new decoration by drawing or sliding it before another. This latter sort is still used, and apparently with much greater success than among the ancients, who were obliged to draw a curtain whenever they made a change in the decoration; whereas on our stage the change is made in a moment, and almost without being perceived.

DECORA'TOR. 8. (from decorate.) An

adorner.

DECO'ROUS. a. (decorus, Lat.) Decent; suitable to a character; becoming (Ray).

To DECORTICATE. v. a. (decortico, Latin.) To divest of the bark or husk (Arbuthnot).

DECORTICATION. 8. (from decorticate.) The act of stripping the bark or husk.

DECO'RUM. 8. (Latin.) Decency; behaviour contrary to licentiousness; seemliness (Wotton).

DECORUM, in architecture, is the suitableness of a building, and the several parts and ornaments thereof, to the station and occasion.

To DECOY. v. a. (from koey, Dutch, a cage.) To lure into a cage; to entrap (L'Estrange).

DECO'Y. 8. Allurement to mischief (Berk

ley).

DECOY, a canal, river, pond, or sheet of water, in a marshy situation, surrounded with reeds, and appropriated to the purpose of taking wild-ducks and teal.. The management of it requires much art, and the decoy-ducks much dexterous training. Wild fowl sleep for the most part during the day, and seek their food towards evening and through the night. Hence as soon as evening sets in the decoy rises, as it is termed, and the sport commences. The machinery consists of a great variety of pipes or tubes terminating in nets, which are called tube or funnel nets; reed-skreens, which are placed at certain intervals along every pipe, and prevent the decoy-man or his dog from being seen, excepting when necessary, and over the whole is suspended a large net upon hoops, extending over the entire pond or decoy space, and open only at one end. Just before the decoy-ducks are ordered by the whistle of the decoy-man, whose sound they know and obey, to commence their alluring stratagems, a small quantity of hemp seeds is thrown over the skreens to tempt the wild-fowl to advance : the trained birds now begin their piping, the wild-fowl make their appearance, and pass slowly, but generally in considerable numbers, over the skreens, and become completely surrounded by the suspended net. If the wildfowl be inactive, the dog receives a signal to paddle a little at a distance, and they are sure to advance in the hope of catching and devouring what they suppose to be small fishes rising to the surface of the water. The decoy-man now rises and makes his appearance at the opening of the net where the wild-fowl entered; they cannot therefore retreat in that direction, and the net effectually prevents them from ascending perpendicularly; they follow therefore the trained birds into the respective pipes, which become narrower and narrower by degrees, so that at last not more than one at a time can pass forwards: another man is secreted at the end of each pipe, who, after suffering the decoy to escape upon the land on which the funnel terminates, receives the rest one after another, and breaks their necks as he

:

receives them in doing which much dexterity seems to be required.

A decoy in some seasons is astonishingly lucrative in 1795 the Tillingham decoy in Essex, at that time in the occupation of Mr. Mascall, netted, after every expense, eight hundred pounds sterling; and the only birds taken were ducks and mallards. In 1799 ten thousand heads of wigeons, teals, and wildducks were caught in a decoy of the Reverend Bate Dudley, in the same county. They are generally contracted for by the London poulterers, who formerly gave eighteen shillings per dozen (which, except in the case of duck and mallard, includes twenty-four, or the double dozen); though the price is now advanced to a guinea or five and twenty shillings.

DECOY-DUCK, a duck that lures others. To DECREASE. v. a. (decresco, Lat.) To grow less; to be diminished (Newton).

To DECREASE. v, n. To make less; to diminish (Daniel).

DECREASE. 8. (from the verb.) 1. The state of growing less; decay (Prior). 2. The wain of the moon (Bacon).

DECREASING PROGRESSION, one whose terms decrease by some regular rule, as the arithmetical progression 9, 7, 5, 3, 1, which decreases by the constant subtraction of the number 2. But the phrase is generally restrained to geometrical serieses, whose terms decrease in a regular proportion: as for example, 1, 1, 4, 4, to, da, d4, &c. and again 1,, 70, &c.

In the first of these examples the sum of all the terms, in infinitum, is 2; the sum of the second progression, in infinitum, is 14. What is here meant, and what ought to be understood in all such cases, is, that, whatever be the number of terms in any such progression, their amount can never equal the determined finite quantity called the sum, though it may approach to it in such a manner, that their difference will become smaller than any assignable quantity. The sum of any infinite geometrical series decreasing, is equal to the square of the first term divided by the differ ence between the first and second, as is demon strated by Malcolm in his Arithmetic. See SERIES.

To DECRE/E. v. n. (decretum, Latin). To make an edict; to appoint by edict (Milton).

To DECRE'E. v. a. To doom or assign by a decree (Job).

DECRE'E, 8. (decretum, Latin.) 1. An edict; a law (Shakspeare). 2. An established rule (Job). 3. A determination of a suit.

DECREE, in the civil law, is a determination that the emperor pronounces upon hearing a particular cause between plaintiff and defendant.

DECREE is a sentence pronounced by the lord chancellor in the court of chancery, and it is equally binding upon the parties, as a judgment in a court of law. By the laws of Enland, a decree (notwithstanding any conhereof) shall not bind the goods or nt only charge the person. If a

decree be obtained and inrolled, so that the cause cannot be reheard, then there is no remedy but by bill of review, which must be on error appearing on the face of the decree, or on matters subsequent thereto, as a release or a receipt discovered since.

DECREES OF COUNCILS are the laws made by them, to regulate the doctrine and policy of the church.

DE/CREMENT. 8. (decrementum, Latin.) Decrease; the state of growing less ; the quantity lost by decreasing (Brown).

DECREMENTS, in mathematics, the small parts by which a variable and decreasing quantity becomes less and less.

DECRE/PIT. a. (decrepitus, Lat.) Wasted and worn out with age (Addison).

To DECRE PITĀTE. v. a. (decrepo, Latin.) To calcine salt till it has ceased to crackle in the fire (Brown).

DECREPITA'TION. (decrepitatio, from decrepo, to crackle.) A kind of crackling noise, which takes place in bodies when heated: it is peculiar to some kinds of salt; which, from a state of solution, are crystallized so rapidly, that the crystals formed burst into minute pieces.

DECRE PITNESS. DECREPITUDE. 8. (from decrepit.) The last stage of decay; the last effects of old age (Bentley).

DECRESCENT. a. (from decrescens, Latin.) Growing less; being in a state of decrease.

DE/CRETAL. a. (decretum, Latin.) Appertaining to a deeree; containing a decree (Ayliffe).

DECRETAL, in the canon law, a letter of a pope determining some point or question in the ecclesiastical law. The decretals composed the second part of the canon-law. The first genuine one acknowledged by all the learned as such, is a letter of pope Siricius, written in the year 385, to Himerus bishop of Tarragona in Spain, concerning some disorders which had crept into the churches of Spain. Gratian published a collection of decretals, containing all the ordinances made by the popes till the year 1150. Gregory IX. in 1227, following the example of Theodosius and Justinian, formed a constitution of his own; collecting into one body all the decisions, and all the causes, which served to advance the papal power; which collection of decretals was called the Pentateuch, because it contained five books.

DECRETIST. s. (from decree.) One that studies the decretal (Ayliffe).

DECRETORY. a. (from decree.) 1. Judicial; definitive (South). 2. Critical; definitive (Brown).

DECRI'AL. 8. (from decry.) Clamorous censure; hasty or noisy condemnation.

To DECRY'. v. a. (decrier, French.) To censure; to blame clamorously; to clamour against (Dryden).

DECUBITUS, in medicine, the manner or posture in which a sick person lies in bed. See MEDICINE.