A C O U 
habitations of the Chinefe, from whence Mr. Aiton ob¬ 
tained it in 1786, by means of Allan Cooper, Efq. com¬ 
mander of the Atlas Indiaman. It flowers in the fpring. 
Propagation and Culture . The fweet-flag will fucceed ve¬ 
ry well in gardens, if the ground be moift; but never pro¬ 
duces its fpikes unlefs it grows in the water. It loves an 
open lituation, and does not thrive well under the lhade of 
trees. The fpik.es of flowers appear towards the latter 
end of June, and continue till Auguft. When this plant 
is fixed in a proper fituation, it will multiply by its creep¬ 
ing roots fall enough.—The Chinefe fweet-grafs mud: be 
kept in a dry Hove, and does not require a great degree of 
heat. 
Acorus ,f. in the materia medica, a name fometimes 
given to the great galangal. See Kempferia. 
Acorus, f in natural hifiory, blue coral. The true 
fort is very fcarce; fome, however, is filhed on the coafis 
of Africa, particularly from Rio del Re to the river of 
the Camarones. This coral is part of the mercfiandile 
which the Dutch trade for with the Camarones: that of 
the kingdom of Benin is alfo very much elleemed. It 
grows in form of a tree on a rocky bottom. 
ACOSMIA,y. An irregularity or dilturbed flate of 
3 T I C S. 8$ 
things, particularly of the critical days of fevers, as 
meant their regular order, from neg. and zotr/A©-, orna¬ 
ment; called alfo madijis, madrotcs. Bald people were call¬ 
ed acofmoi, becaufe they had loft their great ornament. 
Blancard fays it is an ill ftate of health, joined with a lofs 
of colour in the face. 
ACOUSMATICI, f. fometimes alfo called Acouftici, 
in Grecian antiquity, inch of the difciples of Pythagoras 
as had not completed their five years probation. 
ACOUSTIC, adj. [ooisrixa, Gr.J in general, denotes 
any thing that relates to the ear, the fenfe of hearing, or 
the doftrine of founds. 
Acoustic Duct, in anatomy, the fame with meatus 
auditorius, or the external paftage of the ear. 
Acoustic Vessels, in the ancient theatres, were a 
kind of veffels, made of brafs, lhaped in the bell fafhion, 
which, being of all tones within the pitch of the voice or 
even of inftruments, rendered the founds more audible,, 
fo that the adtors could be heard through all parts of thea¬ 
tres, which were even 400 feet in diameter. 
AcousticDiscip l e s, among the ancient Pythagoreans,, 
thofe more commonly called Acousmatici. 
ACOUSTICS. 
A COUSTICS, f. [axas-ir.a, of Gr. to hear.] is a 
fcience w hich inftruifts 11s in the nature of found. 
As no founds can be heard in vacuo , it is evident, that air 
is a vehicle for found. However, we muft not afiert, that 
it is the only vehicle ; for water, metals, and almoft all 
fubftances of any denlity of texture, will not only tranfmit 
found, but even convey it more regularly and perfectly 
than air, which is by no means a good vehicle. Fifties 
have a ftrong perception of founds, even at the bottom of 
deep rivers. From hence, it would feem not to be very 
material in the propagation of founds, whether the fluid 
which conveys them be elaftic or otherwife. One thing, 
however, is certain, that whether the medium be elaftic or 
not, whatever found we hear is produced by a ftroke, which 
the founding body makes againft the fluid, whether air or 
water. The fluid being ftruck upon, carries the impref- 
fion forward to the ear, and there produces its fenfation. 
But the manner in which this conveyance is made, is ftill 
difputed. Whether the found be diffufed into the air, in 
circle beyond circle, like the waves of water when we dif- 
turb the fmoothnefs of its furface by dropping in a ftone; 
or whether it travels along, like rays diffufed from a cen¬ 
tre, fomewhat in the fwift manner that electricity runs 
along a rod of iron ; are queftions which have greatly di¬ 
vided the learned. 
Newton was of the firft opinion. He has explained the 
progreflion of found by an undulatory, or rather a vermi¬ 
cular, motion in the parts of the air. If we have an exaCt 
idea of the crawling of fome infects, we ftiall have a tole¬ 
rable notion of the progreflion of found upon this hypo- 
thelis. The worm for this inftance, in its motion, firft: 
carries its contractions from the hinder part, in order to 
throw its fore part to the proper diftance, then it carries 
its contractions from the fore part to the hinder to bring 
that forward. Something fimilar to this is the motion of 
the air when ftruck upon by a founding body, as the firing 
of an harpfichord fcrewed to a proper pitch, and made to 
vibrate by a ftroke of the finger. From an impreflion thus 
made, there will be an alternate condenfation and relaxa¬ 
tion of the air during the time of One vibration; and, as 
the air going forward ftrikes any oppofing body with great - 
Vol. I. No. 6 
er force than upon retiring, fo each of thefe accelerated 
progreflions has been called by Newton a pulfe of found, 
Thefe pulfes will move every way; for all motion impref- 
fed upon fluids in any direCIion whatfoever, operates all 
around in a fphere: fo that founds will be driven in all 
directions, and will go on fucceeding each other, one on 
the outfide of the other, like circles in difturbed water; 
or rather, they will lie one without the other, like the 
coats of an onion,. 
All who have remarked the tone of a bell, while its- 
founds are decaying away, muft have an idea of thefe pul¬ 
fes of found, which, according to Newton, are formed by 
the air’s alternate progreflion and receflion. And it 
muft be obferved, that, as each of thefe pulfes is formed 
by a Angle vibration of the firing, they muft be equal to 
each other; for the vibrations of the firing are known to 
be fo. 
The velocity with which founds travel, Newton deter¬ 
mines to be in proportion to the thicknefs of the parts of 
the air, and the diftance of thefe parts from each other. 
He proves that each little part moves backward and for¬ 
ward like a pendulum; and demonftrates, that, if the at- 
mofphere were of the fame denfity every where as at the 
furface of the earth, a pendulum, that reached from its 
higheft furface down to the furface of the earth,, would by 
its vibrations difcover to us the proportion of the velocity 
with which founds travel. From hence he calculates, that 
the motion of found will be 979 feet in one fecond. But, 
this not being confonant to experience, betakes in another 
coniideration, namely, vapours in the air ; and then finds 
the motion of found to be 1142 feet in one fecond, or near 
13 miles in a minute; a proportion which experience had ', 
eftabliftied nearly before. 
Various objections, however, have been made to the 
Newtonian Syftem of Sounds. It is urged, that this theo¬ 
ry can only agree with the motion of found in an elaftic 
fluid, whereas founds are known to move forward through 
water, w hich is not elaftic. To explain their progrels 
therefore through water, a fecond theory muft be formed : 
fo that two theories muft be made to explain a fimilar effect; 
which is contrary to true philofophy and the fimplickv of 
Z- nature. 
