Volume 1

A mathematical and philosophical dictionary: containing an explanation of the terms, and an account of the several subjects, comprized under the heads mathematics, astronomy, and philosophy both natural and experimental: with an historical account of the rise, progress, and present state of these sciences: also memoirs of the lives and writings of the most eminent authors. Both ancient and modern, who by their discoveries or improvements have contributed to the advancement of them ... With many cuts and copper-plates / By Charles Hutton.

  • Charles Hutton
Date:
1795-1796
Catalogue details

Licence: Public Domain Mark

Credit: A mathematical and philosophical dictionary: containing an explanation of the terms, and an account of the several subjects, comprized under the heads mathematics, astronomy, and philosophy both natural and experimental: with an historical account of the rise, progress, and present state of these sciences: also memoirs of the lives and writings of the most eminent authors. Both ancient and modern, who by their discoveries or improvements have contributed to the advancement of them ... With many cuts and copper-plates / By Charles Hutton. Source: Wellcome Collection.

    633/696 (page 605)
    Horizontal Plane, in Perfpe6live. See Plane. PIoRizONTAL Proje^ion^ See Projection, and Map. PIoRizoNTAL Range, of a piece of ordnance, is the dillance at which it falls on, or ftrikes the horizon, or on a Horizontal plane, whatever be the angle of eleva- tion or direcfion of the piece. When the piece is pointed parallel to the horizon, the range is then called txie point-blank or point-blanc range. The greatell Horizontal range, in the parabolic theory, or in a vacuum, is that made with the piece elevated to 45 degrees, and Is equal to double the height from which a heavy body mull Ireely fall to acquire the velocity with which the Ihot is difeharged. Thus, a fliot being difeharged with the velocity of v feet per fecond ; becaufe gravity generates the velocity 2g or 32^ feet in the firil fecond of time, by falling 16-/2; g feet, and becaule the fpaces defeended are as the fquares of the velocities, therefore as 4^* i gg. —■ the fpace a body mud defeend to acquire the velocity v of the fhot or the fpace due to the velocity v ; confe- quently the double of this, or — =: is the created . ' . 32? Horizontal range wnth the velocity or at an elevation of 45 degrees ; wdiich is nearly half the fquare of a quarter of the velocity. In other elevations, tlie Horizontal range Is as the fine of double the angle of elevation ; fo that, any other elevation being e. It wall be, as radius i ; fin. le ::—- : —- x fin. 2e, the range at 32I 32f the elevation e, wuth the velocity v. But in a refilling medium, like the atmofphere, the actual ranges fall rar ih.ort of the above theorems, in fo much that wnth the great velocities, the aflual or real ranges may be Itfs than the loth part of the po- tential ranges ; io tiiat feme balls, which actually range, but a mile or two, would in vacuo range 20 or 30 miles. And he.ice .aio it happens that the elevation of the piec-, to Ihoot fartheil m the refilling medium,, is alw^ays below 45°, and gradually the more below it as the velocity Is greater, lo that the greater velocities with w'hich balls are difeharged from cannon wnth gun- powder, require an elevation of the gun equal to but about 30°, or even lefs. And the lets the lize of the balls is too, the lefs mull tins angle of elevation be, to fhoot the fartheil wn'th a given velocity. See Projec- tile, and Gunnery. Horizontal Refradlon. See Refraction. Horizontal Speculum, one to find a horizon at Sea, &c, when the atmofphere is hazy near the hori- zon, by wdiicli the light of it is prevented. A fpeculum of this kind w'as invented by a Mr. Ser- fon, on the principle of a top fpinning, w'hieh alwaiys keeps its iipiight pofition, notwithllanding the m.otiou cf the fubltance it fpins upon. This curious inllru- ment, as it has fmee been improved by Mr. Smeaton, conlids of a well polilhed metal fpeculum, of about 3 inches and a half in diameter, inclofed wuthin a circular rim of brafs ; fo ftted that the centre of gravity of tlic whole fnall fall near the point on wdilch it fpins. This is the end of a Heel axis running through the centre of the fpeculum, above which it finilhes In a: fquare, for the conveniency of fitting a roller on it, which fets it in motion by means of a piece of tape wmund about the roller. Various other contrivances to form artificial horizons have been invented by different perfons, as glafs planes floating on mercury, &c. See Hadley’s Quadrant, and feveral inventions of this fort in the Philof. Tranf. by Elton, Halley, Leigh, 3cc. vol. xxxvii, p. 273, voh xxxviii, p. 167, vol. xl, p. 413, 4175 HORN-Work, in Fortification, a fort of out-work, advancing tow^ard the field, to cover and defend a cur- tin, baftion, or other place, fufpedled to be weaker than the reft ; as alfo to poffefs a height; carrying in the fore-part, or head, two demi-ballions, refembling horns : thefe horns, epaulments, or fiiouldcrings, being joined by a curtIn, Ihut up on the fide by two wings, parallel to one another, are terminated at the gorge of the wmrk, and fo prefent themfelves to the enemy. HOROGRAPHY, the art of making or confiruT- iiig dials ; called alfo Dialling, Elorologlography, Gno- monica, Sclatherica, Photolciatherica, &c. HOROLOGIUM, a common name, among an- cient wTiters, for any inftrument or machine for mea- furing the hours. See Clock, WATCHy- Sun-Dial, Chronometer, Clepsydra, &c. PIOROMETRY, the art of mtafuring or dividing time by hours, and keeping the account of time. EIOROPTER, in Optics, is a right line drawni through the point where the two optic axes meet, pa- rallel to that wdiich joins the centres of the two eyes, or the two pupils. As the line AB drawn through C the point of concourfe of the optic axes of the eyes, and parallel to HI joining the centres of the eyes.— This line is called the Horopter, becaufe it is found to be the limit of diftindl vifion. It has feveral pro])cr- ties in Optics, wdiich are deferibed at large in Aguillo- nius, Opt. lib. 2, difs. 10. flOROSCOPE, in Aftrology, is the afeendant or firll lioufe, being that part of the zodiac which is julE rifmg in the eaftern fide of the horizon at any propofed time, when a fcheme is to be fet or calculated, or a pre- didlion made of anv event. See Ascendant. EIoroscope is alfo ufed for a Ichemc or fio-ure of the ® * • T2 ctkftial houfes ; i. e. the 12 figns of the zodiac, in wdiich is marked the diipofition of the heavens for anv given time. I'hus it is laid, To draw' or conftriRt a HujoJeope oi feheme, And it is more iKculiavlyi calk'd,.