tropical climates, susceptible of cold, feeds upon various vegetables, such as it can procure amidst the barren and sandy wilds which it prefers for its habitation, and burrows with such extreme facility, that, in a state of confinement it will, in no long time, work a passage through a wall of brick. M. Sonnini considers the jerboa as constituting a link between quadrupeds and birds. The beginning of the connection

nosæ.

Asilus Bombylius Culex

Hippobosca Oestrus • Stomoxys.

DIPTERYX, in botany, a genus of the Diadelphia Decandria class and order. Natural order of Papilionacea, or LegumiEssential character: calyx two upper segments winged; legume ovate, compressed, one-seeded. There are two species, viz. D. odorata, Coumarouna, and D. oppositifolia, Taralea. These are both tall trees; about sixty feet high; very much branched at top; the leaves are large, alternate, and pinnate; the leaflets are perfectly entire, two or three on each side, affixed alternately on the mid-rib; the flowers are borne in racemes, which are axillary and terminal; their colour is purple, streaked with violet. The almonds are fragrant, and are put by the Creoles into chests, in order to drive away insects, as well as for the sake of their smell. They are both natives of South America.

DIPUS, the jerbou, in natural history, a genus of Mammalia, of the order Glires. Generic character: two front teeth in the upper and in the under jaw; fore legs very short, hind legs very long; clavicles in the skeleton; tail long and tufted at the tip. Shaw enumerates six species, and Gmelin

ten.

D. sagitta, or the Egyptian jerboa of Pennant, is about the size of a rat, and was known to the ancients by the name of the two-footed mouse. It is to be met with in various parts of Africa, and in the eastern provinces of Siberia. In its posture and movement it greatly resembles a bird. It stands on its hind feet, and rarely applies its fore feet to the ground, employing them almost exclusively in applying food to its mouth, in the same manner as the kangu roo. It inhabits subterraneous apartments prepared by itself, or found accommodated for its purpose, and reposes in them during the greater part of the day, choosing the night for excursion and food. It is, in the

sidered by Shaw as formed by the jerboa, and the last link as completed in the bat. In the sand and ruins about Alexandria the jerboa is very frequently to be found. It is, however, extremely shy, retiring on the slightest alarm to its habitation, and the common mode of destroying them among the Arabs, as related by Somini, is by stopping up all the accesses to their residence but one, and watching their egress at that. In Egypt they are used as food. M. Sonnini kept several in a cage for a considerable time, feeding them on walnuts and other fruits. They appeared extremely fond of basking in the sun, and indeed, in the sun-shine, were often extremely alert and playful. They were mild in their dispositions even in feeding, shewing no tendency to quarrelsomeness, or ferocity; but, on the other hand, they exhibited little or no susceptibility of gratitude or attachment, of joy or fear, and their manner were characterized by a cold and stupid indiffer

ence.

See Mammalia, Plate IX. fig. 5.

D. Canadensis, or the Canada rat. This is the smallest species of the jerboa, being about the size of a mouse. General Davies had several specimens in his possession, and his account of this curious animal is to be found in the fourth volume of the transac tions of the Linnean Society. In company with several other gentlemen, the General caught one of these jerboas in a large field, after an hour's chase, during which the little creature took the extraordinary leaps of from three to five yards in almost uninterrupted successions, sinking, however, at length, under fatigue from such wonderful exertions. Its food could not be ascer tained by the General, who offered it a great variety, no article of which it ap peared at all disposed to touch, and the day after its seizure it died, overwhelmed, probably, by its extreme efforts to escape from its pursuers. It is sometimes found dor mant, and in this state, probably, passes the winter in the rigorous climate of Ca nada. A specimen of it in this state was

brought to the General, after having been found by a labourer, whose spade struck against a substance about the size of a cricket ball, which, on examination, was found to inclose a jerboa, completely rolled up, and in a state of torpor. The ball was found about a foot and a half under the surface of the ground, was perfectly smooth internally, and about an inch in thickness. This case, which was composed of clay, was somewhat mutilated by the accidental blow of the workman, but was deposited by the General, with its contents, in his room, in a small box supplied with some cotton, in hopes that, as the warm season advanced, the animal would revive from its suspended vitality. This hope, however, was not gratified. As the jerboa is not seen in Canada from October till May, it may be concluded that it passes the winter in this curious envelope. See Mammalia, Plate IX. fig. 6.

DIRCA, in botany, a genus of the Octandria Monogynia class and order. Natural order of Vepreculæ. Thymelææ, Jussieu. Essential character: calyx none; corolla tubulons, with an obscure border; stamina longer than the tube; berry one-seeded. There is only one species, viz. D. palustris, marsh-leatherwood, a native of North Ame

rica.

DIRECTION, in mechanics, signifies

the line or path of a body's motion, along which it endeavours to proceed, according to the force impressed upon it.

DIRECTOR, in commercial polity, a person who has the management of the af. fairs of a trading company: thus we say, the directors of the India company, Southsea company, &c.

DIRECTOR, in surgery, a grooved probe, to direct the edge of the knife or scissars, in opening sinuses, or fistulæ, that by this means the subjacent vessels, nerves, and tendons may remain unhurt.

the simple words have, as disoblige, disobey, &c. or to signify a separation, detachment, &c. as disposing, distributing, &c.

DISA, in botany, a genus of the Gynandria Diandria class and order. Natural order of Orchideæ. Essential character: spathe one-valved; petals three, two-parted, gibbous at the base. There are four species. These are all natives of the Cape. DISABILITY, an incapacity in a man to inherit or take a benefit which otherwise he might have done, which may happen four ways; by the act of the ancestor, by the act of the party, by the act of law, and by the act of God. 1. Disability by the act of the ancestor; as, if a man be attainted of treason or felony; by this attainder his blood is corrupt, and himself and his children disabled to inherit. 2. Disability by the act of the party himself; as if one make a feoffment to another who then is sole, upon condition that he shall enfeoff a third before marriage, and before the feoffment made, the feoffee takes a wife; he hath by that disabled himself to perform the condition according to the trust reposed in him, and therefore the feoffer may enter and oust him. 3. Disability by act of law, is when a man by the sole act of the law is disabled, as an alien born, &c. 4. Disability by the act of God, is where a person is of non-sane memory, and in cases of idiocy, &c. But it is a maxim in our law,

ceived to disable his own person. that a man of full age shall never be re

DISANDRA, in botany, a genus of the Heptandria Monogynia class and order. Natural order of Pediculares, Jussieu. Essential character: calyx seven-leaved; corolla seven-parted, flat; capsule two-celled. There are two species, viz. D. prostrata, trailing disandria, and D. africana; the former a native of Madeira, the latter of

Africa.

DIRIGENT, or directrix, a term in geometry, signifying the line of motion, along which the describent line or surface is carried in the genesis of any plane or solid figure.

DIS, an inseparable particle prefixed to divers words, the effect whereof is either to give them a signification contrary to what

called digits: in a total eclipse of the luminaries, the whole disc is obscured; in a partial eclipse, only a part thereof.

DISCORD, in music, a dissonant and inharmonious combination of sounds, so called in opposition to the concord. Among various other discords are those formed by the union of the fifth with the sixth, the fourth with the fifth, the seventh with the

eight, and the third with the ninth and seventh.

DISCOUNT, a compensation for the advance of money which is not due till after a certain period. The person advancing the money, had he retained it, might have made in the given time a certain rate of interest; therefore if he advances it for the use of another, it is equitable that he should be allowed the same gain as he would have made by retaining it in his own hands during the time for which it is lent. Thus, if a person is entitled to 100%. at the end of a year, and has occasion for the money immediately, the sum that ought to be given as an equivalent thereto, allowing 5 per cent interest, is 951. 4s. 94d.; for the discount of 41, 158. 24d, which is then retained, will, if improved at 5 per cent interest, amount at the end of a year to 51. and consequently the lender having then 105. will have made the same gain as he would have made by retaining the money. This is the true principle of discount, according to which the tables published by Mr. Smart are computed; but in commercial transactions, the general mode is, to deduct from the sum to be discounted, the simple interest on that sum for the time for which it is advanced. Thus, if 100l. is payable at the end of six months, the discount deducted is 21. 10s. being the half of a year's interest; or, if 100l. is payable at the end of one month, the discount deducted is 8s. 4d. being the twelfth part of a year's interest. By this means, although the legal rate of interest to be received for money lent is restricted to 5 per cent, the person who employs his money in discounting, makes a greater rate of interest, and the shorter the periods are for which he discounts, the greater his annual gains. In discounting bills of exchange, the days of grace are included in the time the bill has to run, the discount being calculated to the day on which the money is receivable.

Discounting of bills of exchange is one of the modes in which bankers employ the money placed in their hands: they generally discount at 5 per cent, but in time of peace, when the current prices of the public funds are high, they are often willing to discount at 44 or 4 per cent. The bank of England, and other public banks, likewise employ very considerable sums in discounting: the Bank of England never discount any bills which have more than 65 days to run.

Discount is likewise used for certain

customary allowances made by manufac turers and wholesale dealers, to those who purchase goods of them in order to sell retail. In some trades this discount is merely in lieu of credit, in others it is made on all goods sold, whether for immediate payment, or on credit; and is very different on different articles, being on some not more than 1 or 2 per cent, while on others it amounts to 50, and sometimes more than 60 per cent.

DISCRETE, or Disjunct Proportion, is when the ratio of two or more pairs of numbers or quantities is the same, but there is not the same proportion between all the four numbers. Thus, if the numbers 3:6:: 8:16 be considered, the ratio between 3:6 is the same as that between 8:16, and therefore the numbers are proportional; but it is only discretely or disjunctly, for 3 is not to 6 as 6 to 8; that is, the propor tion is broken off between 8 and 3, and is not continued as in the following continual proportionals, 3: 6 :: 12:24.

DISCRETE quantity, such as is not continuous and joined together. Such is a number whose parts being distinct units, cannot be united into one continuum ; far in a continuum, there are no actual determinate parts before division, but they are potentially infinite.

DISCUSSION, in matters of literature, signifies the clear treating or handling of any particular point, or problem,' so as to shake off the difficulties with which it is embarrassed: thus we say, such a point was well discussed, when it was well treated of and cleared up.

DISEASE, in medicine, the state of a living body, wherein it is deprived of the exercise of any of its functions, whether vital, natural, or animal. See MEDICINE.

DISGUISE, a counterfeit habit. Persons doing unlawful acts in disguise, are by our statutes sometimes subjected to great penalties, and even declared felons. Thus by an act, commonly called the black act, persons appearing disguised and armed in a forest, or grounds inclosed, or hunting deer, or robbing a warren or a fish-pond, are declared felons.

DISH, among miners, denotes a wooden measure, wherein they are obliged to measure their ore it is kept by the barmaster, and contains about 672 solid inches.

DISJUNCTIVE proposition, in logle, is that where of several predicates we affirm one necessarily to belong to the subject to the exclusion of all the rest, but leave that par