Page:Cyclopaedia, Chambers - Volume 2.djvu/625

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1y attainted, were to lofe their faid Liveries, and forfeit their Fees tor ever.

• Edward IV. added a fpecial Penalty of five Pounds per Month on every Man that gave fuch Livery, and as much on every Per- fonCoretam'd, either by Writing, Word, or Oath. — But moft of the Statutes are repealed by a Statute 3 Car. I.

RETENTIO, Retinentia, in our Law Books, is fometimes ufed to fignify Retinue. See Retinue.

RETENTION, Retentio, a Faculty of the human Mind, whereby in order to a farther Progrefs in Knowledge, it keeps or retains thofe fimple Ideas which it before received by Senfati- fation or Reflection. See Faculty, Idea, &c.

This is done two ways— Firft, by keeping the Idea which is brought into the Mind for fome time adtually in view ; called Conteniplat'wi. See Contemplation.

Secondly, By reviving thofe Ideas in our Minds, which have difappeared, and have been, as it were, laid out of fight: this is Memory, which is, as it were the Repofitory of our Ideas. See Memory.

Our Ideas being nothing but actual Perceptions in the Mind, which ceafe to be any thing, when there is no Perception of them ; this laying up of our Ideas in the Repofitory or the Memo- ry, amounts to no more than this, that the Mind has a Power in many Cafes to revive Perceptions it once had y with this addi- tional Perception annexed to diem, that it has had them before. See Perception,

It is by the Affiftance of this Faculty, that we are faid to have all cbofe Ideas in our Underftanding- which we can bring in fight, and make the Objects of our Thoughts, without the help of - thofe feniible Qualities, which firib imprinted them there. See Understanding.

Attention and Reperirion help much to the fixing Ideas in our Memories ; but thofe which make the deepen; and moft lading Impreffions, are fuch as come accompanied with Pleafure and Pain. — Ideas but once taken in, and never again repeated, are foon loft; as thofe of Colours, in fuch as lofe their Sight when very young.

The Memory in fome Men is tenacious, even to a Miracle ; but yet there feems to be a conftant Decay of all our Ideas, e- ven of thofe which are ftruck deepeft; and in Minds the moft Retentive : So that if they be not fometimes renew'd, the Print wears out, and at laft there remains nothing to be feen. See Trace.

Thofe Ideas which are often renewed by a frequent Return of the Objects or Actions that produce them, fix themfelves beft in the Memory, and remain Iongeft there : Such are the original Qualities of Bodies; viz. Solidity, Extenfion, Figure, Motion,^, and thofe that almoft conftantly affect us, as Heat and Cold ; and thofe that are the Affections of all kinds of Beings, asExiftence, Duration, Number; which are feldom quite loft, while the Mind retains any Ideas at all. See Quality, Habitude, <&c>

Retention, is alfo ufed in Medicine, &c. for that State of Contraction in the Solids, or vafcular Parts of the Body, which makes them hold fall their proper Contents. See Solid, Ves- sel, &c.

In this Senfe Retention ftands oppofed to Evacuation, or Excre- tion. See Evacuation and Excretion.

Retention and Excretion make one of the fix Non-Naturals. See Non-Natural.

Retention is frequently confidered as a Diforder ; and defined the Act of retaining the Excrements, Humours, &c. fo as they cannot be voided out of the Body. See Excrement.

A Retention of Urine is very painful and dangerous. See Urine.

'Tis a Rete?ithn of peccant Humours which caufes fuch a Diieafe.

RETIARII, in Antiquity, a kind of Gladiators. See Gla- diator.

The Retiarii were denominated from Rete, a Net which they made ufe of againft their Antagonift, who was call'd Secutor, Fol- lower. See Secutores.

This Net rhey carried under their Buckler, and when oppor- tunity ferv'd, caft it on the Head of their Antagonift, and in this . condition kill'd him with a Trident which they bore in the other Hand.

Lipfus, &c. obferve that they fought in Tunics, and were fur- nifhed with Spunges to wipe off the Sweat, Blood, &e. and to ftop their Wounds.— The Word is form'd from the Latin, Rete, net; or, perhaps from Retejaculum, for they call'd their Net, Ja- tuhm, and fometimes in one Word, Retejacuhm. ■ RETICENCY, Reticence, Reticentia, aFigure in Rhe- toric, whereby we make oblique mention of a thing, in pretend- ing to pafs it over unmentioned. See Figure.

Thus : To fay nothing of the Nobility of his Anceftors : I forbear to fpeak of his Courage, and pafs over the Severity of his Morals. See Preteritk>n.

RETICULA, Reticule, in Aftronomy, a Contrivance for the exact meafuring of the Quantity of Eclipfes; introduced a- bout fifty Years ago by the Royal Academy of Paw. See Eclipse.

The Reticule is a little Frame, confifting of thirteen fine filken Threads, equidiftant from each other, and Parallel; placed in the Focus of object Glaffes of Telefcopes; that is, in the Place where the Image of the Luminary is painted, in its full Extent.— Of Con-

fequence, therefore, the Diameter of the Sun or Moon is hereby feen divided into twelve equal Parts or Digits,- fo that to find the Quantity of the Eclipfe, there is nothing to do but to Num- ber the luminous and the dark Parts. See Digit.

As a Square Retic/e is only proper for the Diameter, not for the Circumference of the Luminary. 'Tis fometimes made Cir- cular, by drawing fix concentrick equi-diftant Circles, which re- prefent the Phafes of the Eclipfe perfectly.

But 'tis vifible that the Reticule, whether fquare or circular, ought to be perfectly equal to the Diameter or Circumference of the Star, fuch as it appears in the Focus of the Glafs; otherwife the Divilion cannot be juft.

Now this is no eafy Matter to effect) by reafbn the apparent Diameter of the Sun and Moon differ in each Eclipfe; nay that of the Moon differs from it felf in the Progrefs of the fame Eclipfe.

Another Imperfection in the Reticule is, that its Bignefs is de- termined by that of" the Image in the Focus ; and of confequence will only fit one certain Magnitude.

But M. de la Hire has found a Remedy for all thefe Inconve- niences,* and contrived that the fame Reticule ihall ferve for all Telefcopes, and ail Altitudes of the Luminary in the fame Eclipfe. — The Principle whereon his Invention ftands, is, that two Ob- ject-Glalfes applied againft each other, having a common Focus., and there forming an image of a certain Magnitude; this Image will increafe in Proportion as the Diftance between the two Glaffes is increas'd, as far as a certain Limic.

If then a Reticule be taken of fuch Magnitude as juft to com- prehend the greateft Diameter the Sun or Moon can ever have in the common Focus of two Object- Glaffes applied to each other; there needs nothing but to remove them from each o- ther, as the Star comes to have a leis Diameter, to have the I- mage ftiil exactly comprehended in the fame Reticule.

Another Improvement is, that whereas the filken Threads are fubject to fwerve from the Parallelifm, &c. by the different tem- perature of the Air ; a Reticule may be made of a thin Looking- Glafs, by drawing Lines or Circles thereon, with the fine Point of a Diamond; which fhall be fate from any Alteration of the Air.

RETICULAR B^, tV/7« Reticulars, in Anatomy, a Bo- dy of Veffels lying immediately under the Cuticle or Scarf-Skin. See Cuticle, &c.

Thefe Veffels contain a mucous Liquor, from the Tincture whereof Malpighi imagines the Colour of the Skin to be derived ; founding his Conjecture on this, that the Cutis as well as Cuticle cf Blacks, is white; and that they differ in no other Circumflance from thofe of Europeans, but in this particular. See Negro. See alfo Cutis and Papilla.

RETICULARIS Plexus, in Anatomy, the Choroides. See Choroides.

'Tis thus call'd becaufe the Fibres are interwoven like a Nee.

RETICULUM, the Caul, or Omentum; a Name fometimes given from its Net-like Structure. See Omentum.

RETIFORMIS Lads, in Anatomy, the fame with Rete Mi- rabile. See Rete.

RETINA, in Anatomy, and Opticks, one of the Tunics of the Eye ; call'd alfo Amphibkjlroides, retiformis, and reticularis, as being wove in manner of a Net. See Tunic and Eye.

The Retina is the laft or innermoft of the Coats of the Eye* lying immediately under the Choroides. See Choroides.

'Tis form'd of an Expanfion of the medullary Part of jhe Op- tic Nerve ; whence, it is found very thin, foft, white, &c, re- fembling theSubftance of the Brain, with the traufparency of the Horn of a Lanthom. See Optic Nerve. — When feperated from the Choroides, it runs into a mucous Mafs, or Lump.

The Retina is ufually fuppofed to be the great Organ of Vill- on, which is effected by means of the Rays of Light reflected from each Point of Objects, refracted in their Paifage through the aqueous vitreous and cryftallin Humours, and thus thrown on the Retina; where they paint the Image of the Object; and where they make an Impreftion, which is continued thence, by the fine Capillaries of the Optic Nerves, to the Senfory. See Vision.

Indeed, whether the Retina or the Choroides be the " princi- pal Organ of Vifion, and that whereon the Images of Objects are reprefented ; has been much controverted between feveral Members of the French Academy, particularly Meff Mariotte, Pecquet, Perrault, Mery, and de la Hire.

Mariotte firft ftood up for the Choroides, and was feconded by Mery; the reft afferted the Rights of the Retina.

The Retina wps always judg'd to have all the Characters of the principal Organ .—-'Tis lituate in the Focus of the Refracti- ons of the Humours of the Eye; and of Confequence receives the Vertices of the Cones of Rays, proceeding from the feveral Points of Objects. It is very thin, and confequently very fenfi- ble. It has its Origin from the Optic Nerve ; and is it felf whol- ly nervous, and 'tis the common Opinion that the Nerves arc the Vehicles of all Senfations- Laftly, It communicates with the Subftance of the Brain, where all Senfations terminate. See Brain, Sensation, &c.

As to the Choroides, its ufe was fuppofed to be to ftop the Rays, which the extreme tenuity of the Retina fhould let pafs;

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