p ACC 
Spices quicken the pulfe, and accelerate the motion of the 
blood, and diffipate the fluids; from whence leannefs, 
pains in the ftomach, loathings, and fevers. Arbuthnot.— 
It is generally applied to matter, and tiled chiefly in phi- 
lofophical language ; but it is fometimes ufed on other oc¬ 
casions.—It may point out to a (Indent now and then, what 
may employ the mod ufeful labours of his thoughts, and 
accelerate his diligence in the mod momentous enquiries. 
Waits. 
ACCELERATION,^ \acceleratio, Lat.] The aft of 
quickening motion. The (late of the body accelerated or 
quickened in its motion. The aft of haftening.—Confl- 
dering the languor enfuing' that action in forne, and the 
vifible acceleration it nraketh of age in molt, we cannot but 
think venery very much abridgeth our days. Brown. 
Acceleration, in mechanics, the increafe of velo¬ 
city in a moving body. Accelerated motion is that which 
continually receives frefli acceflions of velocity. Accele- 
rationltands direCtly oppofed to retardation, which denotes 
a diminution of velocity. It is chiefly ufed in phyflcs, in 
refpeCt of falling bodies, i. e. of heavy bodies tending to¬ 
wards the centre of the earth by the force of gravity. 
That natural bodies are accelerated in their defcent, is 
evident from various conliderations, both d priori and 
■pofieriori. Thus, we adlually find, that the greater height 
a body falls from, the greater impreflion it makes, and 
the more vehemently does it Hr ike the fubjeCt plane, or 
•other obllaciev 
Various were the fyltems and opinions which phiiofo- 
phers produced to account for this acceleration. But the 
immediate caule of acceleration is now futficiently obvi¬ 
ous ; the principle of gravitation, which determines the 
body to defeend, determining it to be accelerated by a ne- 
ceflary confequence. 
Suppofe a body let fall from on high : the primary caufe 
of its beginning to defeend is doubtlefs the power of gra¬ 
vity; buc when once the defcent is commenced, that date 
•becomes in feme meafure natural to the body; fo that, if 
left to itlelf, it would perfevere in it for ever, even though 
the firft caufe fliould ceafe: as we fee in a Hone cad with 
the hand, which continues to move after it is left by the 
caufe that gave it motion. But, betide the propenlity to 
defeend imp re (Ted by the fi-rfi caufe, and which of itfelf 
were fuffic'ient to continue the fame degree of motion, 
once begun, in infinitum ; there is a conllant acceflion of lub- 
fequent efforts of the fame principle, gravity, which Con¬ 
tinues to a6t on the body already in motion, in the fame man¬ 
ner as if it were at reft. Here, then, being a double caule 
of motion; and both afting in the fame direction, viz. di¬ 
rectly towards the centre of the earth; the motion they 
jointly produce mult necefTarily be greater than that of 
any one of them.—-And the velocity thus inereafed having 
the fameoaufe of increafe (till peril (ting, the defcent mult 
neceffarily be continually accelerated. 
Acceleration of Bodies on inclined Planes. The 
■fame general law obtains here as in bodies falling perpen¬ 
dicularly : the effect of the plane is to make the motion 
flower; but the inclination being every where equal, the 
retardation ariling therefrom will proceed equally in all 
parts, at the beginning and the ending of the motion. 
See Mechanics. 
Acceleration of the Motion of Pendulums, 
The motion of pendulous bodies is accelerated in their 
■defcent; but in a lefs ratio than that of bodies falling per¬ 
pendicularly. See Mechanics and Pendulum. 
Acceleration of the Motion of Projectiles. 
See Projectile. 
Acceleration is alfo applied in the ancient agrono¬ 
my, in refpeCt of the fixed flars. This acceleration was 
the difference between the revolution of the primum mobile 
and the loiar revolution; which was computed at three 
minutes and fifty-iix feconds. 
Acceleration of a Planet. A planet is faidto be 
accelerated in its motion, when its real diurnal motion ex¬ 
ceeds its mean diurnal motion. And, on the,othcr hand, 
ACC 
the planet is faid to be retarded in its motion, when the 
mean exceeds the real diurnal motion. This inequality 
arifes from the change in the diftance of the planet from 
the fun, which is continually varying; the planet moving 
always quicker in its orbit when nearer the fun, and flow¬ 
er when farther off. 
Acceleration of the Moon, a term ufed to exprefs 
the increafe of the moon’s mean motion from the fun. 
Compared with the diurnal motion of the earth ; fo that it 
is now a little fwifter than it was formerly. Dr. Halley was 
the firfl who made this difeovery: and he was led to it by 
comparing the ancient eclipfes obferved at Babylon with 
thofe obferved by Albatennius in the ninth century, and 
fome of his Own time. He was not able to afeertain the 
quantity of this acceleration, becaufe the longitudes of 
Bagdad, Alexandria, and Aleppo, where the obfervations 
were made, had not been accurately determined. ' But 
lince his time the longitude of Alexandria has been afccr- 
tained by Chazelles; and Babylon, according to Ptolemy’s 
account, lies 50'eaft from Alexandria. From thefe data, 
Mr. Dunthorne compared feveral ancient and modern 
eclipfes, with the calculations of them, by his own tables, 
and hereby verified Dr. Halley’s opinion; for he found 
that the fame tables reprefent the moon’s place more 
backward than her true place in ancient eclipfes, and more 
forward than her true place in later eclipfes; and thence 
juflly inferred, that her motion in ancient times was flow¬ 
er; in later times quicker, than the tables give it. But 
he did not content himfelf with merely afeertaining the 
faCt; he proceeded to determine the quantity of the acce¬ 
leration; and by means of the molt ancient eclipfe of 
which ary authentic account remains, obferved at Baby¬ 
lon in the year before Chvifl 711, he concluded, that the 
obferved beginning of this eclipfe was not above an hour 
and three-quart rs before the beginning by the tables; 
and therefore the moon’s true place could precede her 
place by computation but little more than 50' of a degree 
at that time. Adhiitting the acceleration to be uniform, 
and the aggregate of it as the fquare cf the time, it will 
be at the rate of about to" in 100 years. 
Dr. Long attributes the acceleration above deferibed to 
one or more of thefe caufes:—ei her, 1. The annual and 
diurnal motion of the earth continuing rhe fame, the moon 
is really carried round the earth with a greater velocity 
than heretofore: or, 2. The diurnal motion of the earth, 
and the periodical revolution of the moon, continuing the 
fame, the annual motion of the earth round the fun is a 
little retarded; which makes the fun’s apparent motion in 
the ecliptic a little flower than formerly; and, consequent¬ 
ly, the moon, in palling from any conjunction with the fun, 
fpends lefs time before (lie again overtakes the fun, and 
forms a fubfequent conjunction: in both thefe cafes, the 
motion of the moon from the fun is really accelerated, and 
the fynodical month actually (hortened. Or, 3. Ihe an¬ 
nual nic ion cf the earth, and the periodical revolution 
of the moon continuing the fame, the rotation of the 
earth round its axis is a little retarded : in this cafe, days, 
hours, minutes, feconds, See. by which all periods of time 
mult be meafured, are of a longer duration; and conse¬ 
quently the fynodical month will appear to be fnortened, 
though it really contains the fame quantity of abfolute 
time as it always did. If the quantity of matter in the 
body of the fun be leflened by the particles of light con¬ 
tinually dreaming from it, the motion of the earth round 
the fun may become flower: if the earth encreafes in 
balk, the motion of the moon round the earth may be 
quickened thereby. See Astronomy. 
ACCELERATOR, /! in anatomy, the name of twa 
mufcles of the penis, which ferve for ejecting the urine 
or fefneri. See Anatomy. 
To ACCEND, v. a. [ acctndo , Lat.] To kindle, tofet on 
fire; a word very rarely ufed. 
ACCENDENTES, a lower order of minifters in the 
Romifli church, whole office is to light and trim the can¬ 
dles. 
ACCENDONESj 
