A C C
( 1* )
A C C
- . g. by half ; then the Dentures of the Figure would be
proportionably fmaller ; and it would approach fo much the nearer to a Triangle.— If they were infinitely fmall, l. e. if the Acccffions of Velocity were fuppofed to be made continu- ally, and in every Point of Time, as is really the Cafe ; the Reftangles thus fuccefiively produced will make a lull Tri- angle, e.g. ABE, (Fig. 63.) Here > ,he who1 ^ T "? e
A B, confining of the little Portions of Time A i, A :, SSc. and the Area of the Triangle ABE, of the Sum of all the little triangular Surfaces anfwering to the Divifions of the Time : The whole Area ot Triangle cxpreHes the Space moved thro' in the whole Time A B ; and the little Triangles A if, &c. the Spaces gone thro' in the Divifions ot lime
But thefe Triangles being fimilar, their Areas are to one another, as the Squares of their homologous Sides AB, Ai, ££c. and confcqucntly, the Spates moved, are to each other as the Squares of the Times.
Laws of Acceleration.
Hence we eafily infer the great Law of deceleration, viz. " That a defcending Body uniformly accelerated,^ defcribes, " in the whole Time of its Defcent, a Space which is juft " half of what it would have defctibed in the fame Time, " with the accelerated Velocity it has acquir'd at the End " of its Fall."
For, the whole Space the falling Body has moved thro' in the Time A B, we have already fliewn, will be reprefented by the Triangle ABE; and the Space the fame Body would move thro' in the fame Time, with the Velocity B E, will be reprefented by the Rectangle ABE F — But the Tri- angle is known to be equal to juft half the Rectangle. — Therefore, the Space moved, is juft half of what the Body would have moved with the Velocity acquir'd at the End of the Fall.
Coroll. Hence, i°, we gather, that the Space moved
with the laft acquired Velocity B E, in half the Time A B ; is equal to that really moved by the falling Body in the whole Time AB.
2°, If a falling Body defcribe any given Length in a given Time, in double that Time it will defcribe four times that Length ; in thrice the Time, nine times, gJc. and univer- fally, if the Times be in Atithmetical Proportion, 1,2, 3, 4, J5?c. the Spaces defcribed will be 1, 4, 9, icf, t>c.
3 , The Spaces defcribed by a falling Body, in a Series of equal Moments or Intervals of Time, will be as the une- qual Numbers 1, 3, 5, 7, 9, &c— And fince the Velocities acquir'd in falling are as the Times ; the Spaces will alfo be as the Squares of the Velocities ; and both Times and Ve- locities in a fubduplicate Ratio of the Spaces.
The Motion of a Body afcending, or impell'd upwards, is diminifli'd or retarded from the fame Principle of Gravity acting in a contrary Direction, in the fame manner as a fall- ing Body is accelerated. See Retardation.
A Body thus projected upwards, rifes till it has loft all its Motion ; which it does in the fame Time that a Body fall- ing would have acquir'd a Velocity equal to that wherewith the Body was thrown up.
And hence, the fame Body thrown up, will rife to the fame height, from which, falling, it would have acquir'd the Velocity wherewith it was thrown up.
And hence, the Height which Bodies thrown up with different Velocities do aicend to, are to one another as the Squatcs of thofe Velocities.
Acceleration of Bodies on inclined Tlanes. — The fame general Law obtains here, as in Bodies falling perpendicu- larly : The Effect of the Plane is, to make the Motion flow- er 5 but the Inclination being every where equal, the Retar- dation rifing therefrom will proceed equally in all Parts, at the Beginning and the Ending of the Motion.— The par- ticular Laws, fee under the Article Inclined Plane.
Acceleration of the Motion of 'Pendulums. — The Mo- tion of pendulous Bodies is accelerated in their Defcent ; but in a lefs Ratio than that of Bodies falling perpendicu- larly. Sec the Laws thereof under the Article Pendulum.
Acceleration of the Motion of 'ProjeBiles. See Pro- jectile.
Acceleration of the Motion of comfreffed "Bodies, in expanding or reftoring themfelves. See Compression, Di- xatation, Tension, Fibre, &c.
That the Motion of comprefs'd Air, expanding it felf by its Elafticity to its former Dimenfions, is accelerated, is evi- dent from various Considerations. See Air, Elasticity,^.
Acceleration is alfo applied in the antient Aftronomy, in refpect of the Fixed Stars. — This Acceleration was the Difference between the Revolution of the Primum Mobile, and the Solar Revolution ; which was computed at 3 Mi- nutes, and 56 Seconds. See Star, Primom Mohile, &c.
ACCELERATOR Urintg, a Mufcle of the Penis, by fome made a Pair of Mufcles ; thus call'd from its Office in expediting the Difcharge of the Urine and Semen. See Musme, Penis, Use
It arifes tendinous from the upper and fore-Part of the Urethra ; but foon grows flefliy, paffes under the Os PuHs, and incompaftes the Bulb of the cavernous Body of the U- rethta. — Both fides of this Mufcle meet in a middle Line, correfponding to the Seam in the Skin over it 5 and continue fo united, the fpace of two Inches ; after which, it deta- ches two flefliy Elongations, which become thin Tendons at their Terminations on the cavernous Bodies of the Penis.
Its upper Part covering the Bulb, when in Acfion, ftreigh- tens the Veins which pals thro' it from the Corpus Caverno- fum of the Urethra 5 and hinder the Reflux of the Blood in an Erection ; and by the repeated Contractions of this upper Part, drives the Blood in the Bulb towards the Glans. See Erection.
The two Elongations comprefs the Channel of the Ure- thra, and fo force out the contain'd Seed, or Urine ; whence the Mufcle takes its Name. See Urine, and Seed.
ACCENSION, Accensio, in Phyficks, the Aft of Kindling, or fetting a Body on Fire. See Fire, Fuel* Heat, &c.
Accenfion, on other Occafions, is sailed Inflammation, Ig- nition, Conflagration, &c. See Ignition, Inflammation, Conflagration, £<?e.
Accenfion ftands oppofed to Extinction. See Extinc- tion.
The Word is form'd of the Latin Accendo, I kindle.
ACCENSUS, a Roman Officer, whereof there were two Kinds.
The firft, were Officers of the Magiftrates ; that is, of the Confuls, Pretors, Proconfuls, S$c. who had their Name, Ac- cenfi, ah acciendo ; their principal Employment being to call Affemblies of the People, and fummon People to appear in Court.
The other Order of Accenfi, were a kind of fupernume- rary Soldiers, kept on foot, to be ready to fupply the Place of thofe who were kill'd or wounded in Battel. — And thefe, according to Afconius <Pedianus, becaufe they were added to the proper Number, were called Accenfi, quia adcenfe- lantur, or accenfeiantur, i. c. ad cenfiim adficielantur.
ACCENT, Accentus, a certain Inflection of Voice ; or a peculiar Tone and manner of Pronunciation, contracted from the Country or Province where a Perfon was bred. See Voice, and Pronunciation.
In this Senfe, we fay, the Welch Tone or Accent, the Northern Accent, the Gafcoign Accent, Norman Accent, &c. See Tone, ££?c.
The Word is form'd of the Latin Accentus ; compounded of ad, and cano, I fing.
Accent is alfo a Tone or Modulation of the Voice, frequently ufed as a Mark of the Intention of the Speaker ; and giving a good or an evil Signification to his Words.
One may give Offence with the fofteft and moft foothing Words imaginable, by a proper Management of the Ac- cent, and manner of rehearfing them.— The Accent fre- quently gives a contrary Senfe to what the Words themfelves naturally imported. See Word, Figure, &c.
The Accent, properly, has only to do with high and low. — Tho the modern Grammarians frequently alfo ufe it in re- fpect of loud and foft, long and fliort ; which confounds Ac- cent with Quantity. See Quantity.
The Difference between the two may be conceiv'd from that which we obferve between the Beat of a Drum, and the Sound of a Trumpet : the former expreffes every thing belonging to loud and loft, and long and fliort ; but, fo long as there is a lutmwtn. in the Sound, there is nothing like Accent.
Accent is alfo ufed in Grammar, for a Character placed over a Syllable, to mark the Accent, i. e. to ftiew it is to be pronounced in a higher or a lower Tone, and regulate the Inflexions of the Voice in reading. See Character, Tone, Voice, l3c.
We ufually reckon three grammatical Accents in ordinary ufe, all borrow'd from the Greeks, viz. the Acute Accent, which fliews when the Tone of the Voice is to be raifed ; and is expreffed thus ('). See Acute.
The Grave Accent, when the Note or Tone of the Voice is to be depreffed 5 and is figur'd thus ( ' ). See Grave.
The Circumflex Accent is compofed of both the Acute and the Grave ; it points out a kind of Undulation of the Voice, and is expreffed thus ( A ). See Circumflex.
The Word Accent is alfo applied, fomewhat abufively, to the Characters which mark the Quantities of Syllables ; or the Time the Voice is to dwell on them. See Time.
The fpurious Accents anfwer to the Characters of Time in Mufick ; as Crotchets, Quavers, &c. — The genuine Ac- cents anfwer to the mufical Notes, Sol, fa, &c. See Note, &c.
Such are, the long Accent, which fliews that^ the Voica is to flop on the Vowel, and is expreffed thus ( ").
The
