Page:Cyclopaedia, Chambers - Volume 1.djvu/585

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DIOPTER, or Dioptra, in the Writers of Aflnonomy, is frequently ufed for the Holes pierced in th^/ftnnnlte, or Sights of an Alhidade. See Sights.

DIOPTRA, among Surgeons, is an Inflrument whereby one nwy f« into the Matrix, and infpect any Ulcers there- in call'd alfo Speculum Matricis, and Dilatatorium.

DIOPTRICKS, the Doftrine of refrafted Vifion, calPd alfo Anaclafticks. See Vision.

gjiof tricks is properly the third Branch of Opticks ; Its Office being to confider, and explain the Effects of Light re- fracted by pafling through different Mediums, as Air, Water, Glafs, fSc and efpecially Lens's. See Opticks.

The Word Dioptricks is originally Greek, being form'd of fd,f er > through, and iVJofx*;, I fee ; whence fiovrfnai fhould be to fee through any 'Thing.

'the Za-ws 0/ Dioptricks, fee delivered under the Articles Refraction, Lens, $$c. and the Application thereof, in the Conftrutlion of Telefcopes, ATicrojcopes, and other Dioptrical Infrwnents, under the Articles Telescope, Microscope, $$c.

DIPHRYGES, in Pharmacy, the Scoria, Sediment, or Calx of melted Copper gather'd in the Furnace, when the Metal is runout. See Scoria.

liiofcorides makes three Kinds of Diphryges : One call'd Natural, tho' made ot a Kind of Clay, or Bole dried in the Sun : That made of Marcafflte, or Pyrites burnt ; and that of the Fceces of Copper. See Copper.

It is moderately fnarp, and aflringent, and is reputed good for Ulcers that cicatrize with Difficulty.

The Word is form'd from the Greek fa, tivice, and

tfiyii', t0 raa f r -

DIPLOE, in Anatomy, a fpongy, medullary Subftance, feparating the two Tables of the Cranium, and together with them constituting the Skull. See Cranium.

The Subftance of the Diploe being fpongeous, eafily im- bibes the Blood, and is found feparated into an infinite Num- ber of little Cells of different Magnitudes, which receive little Branches of Arteries from the Brain, and give Paffage to little Veins that proceed to the Sinus's of the dura Aba- ter.

DIPLOMA, an Inflrument given by fome Colleges, and Societies, on Commencement to any Degrees, or pafling Exa- mination, as a Proof of Qualification tor any Advancement to Title, or Power.

DWVY^G-Needle, or Inch 'natory-Needle, a Magnetical Needle, fo hung, as that inftead of playing horizontally, and pointing out North and South, one End dips, or inclines to the Horizon, and the other Points to a certain Degree of Elevation above it. See Needle, and Magnet.

Or, a Dipping-Needle may be defined with Mr. Whifton, to be along flaight Piece of Steel, (reprefented 'Fab. Navi- gation Fig.lll) every way equally pois'd on its Centre, and afterwards touch'd with a Load-Hone 5 but fo contriv'd, as not to play on the Point of a Pin, as does the common ho- rizontal Needle, but to fwing in a Vertical Plane, about an Axis parallel to the Horizon : And this in Order to difco- ver the exact Tendency of the Power of Magnetifm. See Magnetism.

The Inventor of the Dipping-Needle, Mr. Whifton ob- ferves, was, without all Question, an Lugl/ftrman, Robert Norman by Name, a Compafs-maker at Wapping, about the Year 1576 ; which is not only teftificd by his own Account, in his Nenv Attractive ; but was allow 'd by Dr. Gilbert, and other Writers of that Time. The Occafion of the Dif- covery he himfclf relates : viz. that it being his Cuftom to finiih, and hang the Needles of his Compaffes, before he touch'd 'em 5 he always found, that immediately after the Touch, the North-Point would bend, or decline downward, under the Horizon 3 Infomuch, that to balance the Needle again, he was always fore'd to put a Piece of Wax on the South End, as a Counter-poize.

The Conflancy of this Effect led him at Length to obferve the prccife Quantity of the Dip, or to meafure the greater! Angle which the Needle would make with the Horizon.

This in the "Year 1576 he found at London to be 71 50 But the Dip varies as well as the Horizontal Direction ; and is now found, at the fame Place, to be 75 10'.

Burrows, Gilbert, Ridley, Send, &c. endeavour'd to apply this Difcovery of the "Dip, to the finding of the Latitude j and the laft Author, going further, likewife propofed the find- ing of the Longitude thereby : but for Want of Obferva- tions, and Experiments, he could go no length.

Mt.Wiifton, being furnihYd with the further Obftrvations of Col. Wmdham, Dr. Halley, Mr. 'Pound, Mr. Cunning- ham, f ere Noel, Mr. Feuillee, and his own, has improved v ory much on the Doctrine, and Ufe of the Dipping-Needle, brought it to more certain Rules, and endeavour'd in good Earnest to find the Longitude thereby.

In Order to this, he obferves, I. That the true Tendency of the North, or South End of every Magnetic Needle is not to that Point in the Horizon to which the Horizontal Needle points, but towards another directly under it in the fame Ver- tical ; and in different Degrees under it, in different lees and at different Places. " s '

_ II. That the Power by which a Horizontal Needle is govern'd, and all our Navigation ordinarily directed is proy'd to be but one Quarter of the Power, by which the Dipping-Needle is moved ; which mould render the latter far the more effectual, and accurate Inflrument.

III. That a 'Dipping-Needle a Foot long, will plainly ihew an Alteration of the Angle of Inclination in theft Parts of the World in half a Quarter of a Degree, or -j\ Geogra- phical Miles ; /. e. fuppofing that Diftance taken along, of near a Meridian. And a Needle of 4 Foot, in two or three Miles.

IV. A Dipping-Needle 4 Foot long, in theft Parts of the World, will ihew an equal Alteration along a Parallel ; As one of a Foot long will ihew along a Meridian, i. e. this will with equal Exaancfs fhew the' Longitude, as that the Latitude.

This depends on the Pofition of the Lines of equal Dip t in theft Parts of the World, which are found to lye about 14 or 15 Degrees from the Parallels.

Hence he argues, that as we can have Needles of 5, S, 7, 8, or more Feet long, which will move with Strength fufficient for exact Obfervation ; And fince Microfcopes may be ap- plied to the Viewing the fmalleft Divifions of Degrees on the Limb of the Inflrument, it is evident, the Longitude at Land may be found thereby to left than four Miles.

And as there have been many Observations made at Sea with the fame Inflrument by Noel, Feuillee, &c. which have determin'd the Dip ufually within a Degree, fome- times within -j or ^ of a Degree, and this with fmall Needles of 5, or 6, or at the moft p Inches long ; 'tis evi- dent, the Longitude may be found even at Sea, to lefs than half a Quarter of a Degree.

Thus much premis'd, the Obfervation it ftlf follows.

To find the Longitude, or Latitude by the Dipping- Needle :

If the Lines of equal Dip below the Horizon be drawn on Maps, or Sea-Charts, from good Obftrvations, it will be eafy from the Longitude known to find the Latitude • and from the Latitude known to find the Longitude, cither at Sea, or Land.

Suppofe, e.gr. you were travelling, or failing along the Meridian of Loudon, and found the Angle of Dip, with a Needle of one Foot to be 7 5°; the Chart will ihew, that this Meridian, and the Line of Dip meet in the Latitude of 53 11'; which, therefore, is the Latitude fought. See La- titude.

Or, fuppofe you were travelling, or failing along the Paral- lel of London, i.e. in 51° jz North Latitude, and you find the Angle of Dip to be 74. This Parallel, and the Line of this Dip will meet in the Map in 1° 46' of Eaft Lon- gitude from London ; which is, therefore, the Longitude fought. See Longitude.

DIPTERE, or DIPTERON, in the ancient Architecture, a Temple furrounded with two Rows of Columns, which from a Sort of Portico's, cull'd Mings, or I/les. See Temple.

The Word is Greek, form'd from <fi«, twice, and Wtm Ala, Wing. ' '

D1PTHONG, in Grammar, a double Vowel, or the Union, or Mixture of two Vowels pronounced together, fo as only to make one Syllable ; as the Latin ae, or ce, oe, or ce ; the Greek u, the Englifh si, au, &c. See Vowel, and Syllable.

The Latins pronounced the two Vowels in their Dip- thongs much as we do ; with this Exception, that the two were not heard equally, but the one was fomewhat wjaker than the other, tho' the Divifion was made with all the De- licacy imaginable.

Among us, moft of the Latin Dipthongs are loft in the Pronunciation : Their ie and a are only fpoke as e's ; So alfo the Englifh ea, oa, &c. tho' wrote with two Characters, arc pronounced as Ample Sounds.

^ In Englifa, French, and divers other Languages, one may diftinguifh Dipthongs with regard to the Eyes, from Dip- thongs with regard to the Ears.

A Dipthong with regard to the Eye, is form'd of two Vowels meeting in the fame Syllable, whether the particu- lar Sound of each of them be heard in the Pronunciation, whether the Sound of one of them be drown'd j or laftly, whether a new Sound different from either of them refult from both. In the two latter Occasions, 'tis with fome Im- propriety, that we call them Dipthongs. The firit only are real Dipthongs, as being fuch both to the Eye, and Ear.

Dipthongs with regard to the Ear, are either form'd of two Vowels, meeting in the fame S) liable, or whole Sounds