Dionis, credulous, and the bigoted flave of partiality, fatyr, Diona. and flattery. He inveighs against the republican principles of Brutus and Cicero, and extols the caule of Cæfar. Seneca is the object of his fatyr, and he reprefents him as debauched and licentious in his morals.

DIONIS (Peter), a famous furgeon, born at Paris, diftinguished himself by his fkill in his profeffion, and by his works; the principal of which are, 1. A course of operations in furgery; 2. The anatomy of man; and, 3. A treatife on the manner of affifting women in child-birth. He died in 1718.

DIONEA MUSCIPULA, or Venus's Fly-trap, in botany, a newly difcovered fenfitive plant.

Every one fkilled in natural hiftory knows, that the mimofæ, or fenfitive plants, close their leaves, and bend their joints, upon the leaft touch: and this has aftonished us; but no end or defign of nature has yet appeared to us from thefe furprifing motions: they foon recover themselves again, and their leaves are expanded as before. But the plant we are now going to defcribe, fhows that nature may have fome view towards its nourishment, in forming the upper joint of its leaf like a machine to catch food: upon the middle of this lies the bait for the unhappy infect that becomes its prey. Many minute red glands that cover its inner surface, and which perhaps difcharge fome fweet liquor, tempt the poor animal to taste them; and the inftant thefe tender parts are irritated by its feet, the two lobes rise up, grasp it faft, lock the two rows of fpines together, and fqueeze it to death. And further, left the frong efforts for life, in the creature thus taken, fhould ferve to difengage it, three fmall erect spines are fixed near the middle of each lobe among the glands, that effectually put an end to all its ftruggles. Nor do the lobes ever open again, while the dead animal continues there. But it is neverthelefs certain, that the plant cannot distinguish an animal from a mineral fubftance; for, if we introduce a ftraw or a pin between the lobes, it will grafp it full as faft as if it was an infect. The plant is one of the monogynia order, belonging to the decandria clafs. It grows in America, about 35 deg. N. Lat. in wet fhady places, and flowers in July and Auguft. The largeft leaves are about three inches long, and an inch and half a cross the lobes: the glands of those exposed to the fun are of a beautiful red colour; but thofe in the fhade are pale, and inclining to green. The roots are fquamous, fending forth but few fibres, and are perennial. The leaves are numerous, inclining to bend downwards, and are placed in a circular order; they are jointed and fucculent; the lower joint, which is a kind of ftalk, is flat, longifh, two-edged, and inclining to heart-shaped. In fome varieties they are ferrated on the edges near the top. The upper joint confifts of two lobes; each lobe is of a femi-oval form, with their margius furnished with ftiff hairs like eye-brows, which embrace or lock in each other when they clofe: this they do when they are inwardly irritated. The upper furfaces of thefe lobes are covered with fmall red glands; each of which appears, when highly magnified, like a compreffed arbutus "berry.--Among the glands, about the middle of each lobe, are three very fall erect fpines. When the lobes inclofe any fubN° 101.

ftance, they never open again while it continues there. Dianæa If it can be fhoved out fo as not to ftrain the lobes, Dionyfius. they expand again; but if force is used to open them, fo ftrong has nature formed the spring of their fibres, that one of the lobes will generally fnap off rather than yield. The ftalk is about fix inches high, round, fmooth, and without leaves; ending in a fpike of flowers. The flowers are milk-white, and ftand on footstalks, at the bottom of which is a little painted bractea or flower-leaf. The foil in which it grows, as appears from what comes about the roots of the plants when they are brought over, is a black, light, mould, intermixed with white fand, fuch as is ufually found in our moorish heaths. Being a fwamp plant, a northeast aspect will be propereft for it at fift, to keep it from the direct rays of the fun; and in winter, till we are acquainted with what cold weather it can endure, it will be neceffary to shelter it with a bell glass, such as is used for melons. This fhould be covered with ftraw or a mat in hard frofts. By this means feveral of thefe plants have been preserved through the winter in a very vigorous ftate. Its fenfitive quality will be found in proportion to the heat of the weather, as well as the vigour of the plant. Our fummers are not warm enough to ripen the feed; or poffibly we are not yet fufficiently acquainted with the culture of it. In order to try further experiments on its fenfitive powers, fome of the plants might be placed in pots of light moorish earth, and placed in pans of water, in an airy ftove in fummer; where the heat of fuch a fituation, being like that of its native country, will make it furprisingly active.

DIONYSIA, in Grecian antiquity, folemnities in honour of Bacchus, fometimes called by the general name of Orgia; and by the Romans Bacchanalia, and Liberalia. See BACCHANALIA and BACCHUS.

DIONYSIACA, in antiquity, was a defignation given to plays and all manner of sports acted on the ftage; becaufe play-houfes were dedicated to Dionyfius, i. e. Bacchus and Venus, as being the deities of fports and pleasure.

DIONYSIAN PERIOD. See CHRONOLOGY, n° 31. DIONYSIUS I. from a private fecretary became general and tyrant of Syracufe and all Sicily. He was likewife a poet; and having, by bribes, gained the tragedy-prize at Athens, he indulged himself fo immoderately at table from excefs of joy, that he died of the debauch, 386 B. C. but fome authors relate that he was poifoned by his phyficians.

DIONYSIUS II. (his fon and fucceffor) was a greater tyrant than his father: his fubjects were obliged to apply to the Corinthians for fuccour; and Timoleon their general having conquered the tyrant, he fled to Athens, where he was obliged to keep a fchool for fubfiftence. He died 343 B. C.

DIONYSIUS (Halicarnaffenfis), a celebrated hiftorian, and one of the moft judicious critics of antiquity, was born at Halicarnaffus; and went to Rome after the battle of Actium, where he ftaid 22 years under the reign of Auguftus. He there compofed in Greek his Hiftory of the Roman Antiquities, in 20 books, of which the firft 11 only are now remaining. There are alfo ftill extant feveral of his critical works. The best edition of the works of this author is that of

Oxford,

APHORISM S.

1. A ray of light paffing obliquely out of one medium into another that is denfer, will be refracted toward the perpendicular; as the ray AB, by paffing out of air into glafs, is refracted into BF, inclined to the perpendicular AF. On the contrary, a ray paffing out of a denfer into a rarer medium, will be refracted from the perpendicular; as the ray BC, paffing out of the glafs G H into air, is refracted into D I.

2. The fines of the angles of incidence and refraction, when the lines that contain them are all equal, will have a determinate proportion to each other, in the fame mediums: which between air and water will be as 4 to 3; between air and glass, as 3 to 2, nearly; and in other mediums in proportion to their denfities.

3. Any object viewed through a glafs, whofe two furfaces are parallel, will appear of its natural fhape and dimenfions, provided it be only of the fize of the pupil of the eye, and the light proceeding from it be received directly through the glafs by one eye only. In all other fituations an alteration will be perceived not only in its apparent fituation, but its dimenfions alfo. This alteration will be greater in proportion to the thicknefs of the glafs, and the obliquity of the rays; in general,

it is fo fmall as to be overlooked. 4. All the of light which fall upon a convex rays lens, whether parallel, converging, or diverging to a certain degree, will be made to meet in a focus on the other fide; but if they diverge exceffively, they will not do fo. Thus if rays diverge from a point placed before the glass, at the focal diftance from it, they will become parallel after paffing through it; and if the point from which they proceed be nearer the glafs than its focal diftance, they will ftill continue to diverge, though in a lefs degree than before.

5. When parallel rays fall upon a concave lens, they will be made to diverge after paffing through it. If they are diverging already before they fall upon the glafs, they will diverge more after paffing through it; or even if they are converging to a certain degree, they will diverge upon paffing through a concave lens; but if the convergence is very great, they will converge af ter paffing through the glafs, though to a more diftant point than that at which they would otherwife have

met.

6. When an object is viewed through two convex lenfes, its apparent diameter ought to be to its real one as the diftance of the focus of the object-glafs is to that of the eye-glafs; but by reafon of the aberration of the rays of light, the magnifying power will be fomewhat greater or lefs in proportion to the diameter of the object.

By thefe aphorifms we are enabled to account for the various effects of dioptric machines, as refracting telescopes, microfcopes, the camera obfcura, &c. See

OPTICS.

crown; the firft at E, the fecond at F, and the laft at G. Then place a perfon at H, where he can fee no further into the veffel than I and tell him, that by pouring water into the veffel you will make him fee three different pieces of money; bidding him obferve carefully whether any money goes in with the

water.

Here you must obferve to pour in the water very gently, or contrive to fix the pieces, that they may not move out of their places by its agitation.

When the water comes up to K, the piece at E will become vifible; when it comes up to L, the pieces at E and F will appear; and when it rifes to M, all the three pieces will be visible.

From what has been faid of the refraction of light, the cause of this phenomenon will be evident: for while the veffel is empty, the ray HI will naturally proceed in a ftraight line but in proportion as it becomes immerfed in water, it will be neceffarily refracted into the feveral directions NE, OF, PG, and confequently the feveral pieces must become visible.

:

II. Optical Augmentation.

Take a large drinking glass of a conical figure, that is fmall at bottom and wide at top; in which put a fhilling, and fill the glafs about half full with water: then place a plate on the top of it, and turn it quickly over, that the water may not get out. You will then fee on the plate, a piece of the fize of a half crown; and fomewhat higher up, another piece of the fize of a fhilling.

This phenomenon arises from seeing the piece thro' the conical furface of the water at the fide of the glafs, and through the flat furface at the top of the water, at the fame time: for the conical furface dilates the rays, and makes the piece appear larger; but by the flat furface the rays are only refracted, by which the piece is feen higher up in the glafs, but ftill of its natural fize. That this is the cause will be further evi

dent by filling the glafs with water; for as the fhilling cannot be then feen from the top, the large piece only

will be vifible.

III. Optical Subtraction.

AGAINST the wainscot of a room fix three fmall

pieces of paper, as A, B, C, at the height of your eye; and placing yourfelf directly before them, hut your right eye and look at them with the left; when you will fee only two of thofe papers, fuppofe A and B; but altering the pofition of your eye, you will then fee the third and one of the firft, fuppofe A; and by altering your pofition a fecond time, you will fee B and C; but never all three of them together.

The caufe of this phenomenon is, that one of the three pencils of rays that come from thefe objects, falls conftantly on the optic nerve at D; whereas to produce diftinct vifion, it is neceffary that the rays of light fall on fome part of the retina E, F, G, H. We fee by this experiment, one of the ufes of having two eyes; for he that has one only, can never fee three objects placed in this pofition, nor all the parts of one object of the fame extent, without altering the fituation of his eye.

IV. Alternate Illufion.

WITH a convex lens of about an inch focus, look atten

Fig. 5.