acoustics. 
ness of that portion of its stalk, which is 
above the spadix, as well as by all its parts,, 
except the florets, being five times smaller 
than in that plant. It is probably a native 
of China, and cultivated for the sake of its 
smell, in pots near the habitations of the 
Chinese. The sweet flag will succeed very 
well in moist garden ground, but never 
produces its spikes, unless it grows in wa- 
ter. The dried roots of the calamus aro- 
maticus are commonly imported from the 
Levant, though those grown in England are 
equally good. They have a strong aro- 
matic smell, and a warm pungent taste , 
the flavour is much improved by drying. 
The powdered root might perhaps supply 
the place of foreign spices ; and indeed it is 
the only native aromatic plant of northern 
climates. It is carminative and stomachic, 
and often used as an ingredient in bitter in- 
fusions. 
ACOTYLEDONES, in botany, plants 
so called, because their seeds are not fur- 
nished with lobes, and of course put forth 
no seminal leaves. All mosses are of this 
kind. See CotyEebones. 
ACOUSTICS, in physics,- is that science 
which instructs us in the nature of sound. It 
is divided by some writers into diacoustics, 
which explains the properties of those sounds 
that come distinctly from the sonorous body 
to the ear ; and catacoustics, which treats of 
reflected sounds : but this distinction is not 
necessary. In the infancy of philosophy, 
sound was held to be a separate existence; 
it was conceived to be wafted through 
the air to our organs of hearing, which it 
was supposed to affect in a manner resem- 
bling that in which our nostrils are affected 
when they give ifc the sensation of smell. 
Yet, even in those early years of science, 
there were some, and, in particular, the ce- 
lebrated founder of the Stoic school, who 
held that sound, that' is, the cause of sound, 
was only the particular motion of external 
gross matter, propagated to the ear, and 
there producing that agitation of the organ 
by which the soul is immediately affected 
with -the sensation of sound. Zeno says, 
“ Hearing is produced by the air which 
intervenes between the thing sounding and 
the ear. The air is agitated in a spherical 
form, and moves off in waves, and falls on 
the ear, in the same manner as water un- 
dulates in circles when a stone has been 
thrown into it.” The ancients were not re- 
markable for precision, either of concep- 
tion or argument, in their discussions, and 
they were contented with a general and 
vague view of things. Some followed the 
opinion of Zeno, without any farther at- 
tempts to give a distinct conception of the 
explanation, or to compare it with experi- 
ment. But in later times, during the ar- 
dent: researches into the phenomena of 
nature, this became an interesting subject 
of inquiry. The invention of the air-pump 
gave the first opportunity of deciding by 
experiment, whether the elastic undulations 
of air were the causes of sound ; and the 
trial fully established the point; for a bell 
rung in vacuo gave no sound, and one rung 
in condensed air gave a very loud one. It ‘ 
was therefore received as a doctrine in ge- 
neral physics that air was the vehicle of 
sound. The celebrated Galileo, the parent 
of mathematical philosophy, discovered the 
nature of that connection between the' 
lengths of musical, chords aud the notes 
which they produced, which had been ob- 
served by Pythagoras, or learned by him 
in his travels in the East, and which he 
made the foundation of a refined and beau- 
tiful science, the theory of music. Galileo 
shewed, that the real connection subsisted 
between the tones and the vibrations of 
these chords, and that their different de- 
grees of acuteness corresponded to the dif- 
ferent. frequency of their vibrations. Tim 
very elementary and familiar demonstration 
which he gave of this connection, did not 
satisfy the curious mathematicians of that 
inquisitive age; and the mechanical theory 
of musical chords was prosecuted to a great 
degree of refinement. In the course of 
this investigation, it appeared that the chord 
vibrated in a manner precisely similar to a 
pendulum vibrating in a cycloid. It must 
therefore agitate the air contiguous to it in 
the same manner : and thus there is a parti- 
cular kind of agitation that the air can receive 
and maintain, which is very interesting. 
Sir Isaac Newton took up this question 
as worthy of his notice ; and endeavoured 
to ascertain with mathematical precision 
the mechanism of this particular class of un- 
dulations, and gave us the principal theo- 
rems concerning the undulations ot elastic 
fluids, which make the 47, &c. Propo- 
sitions of Book II. of his Principles of Na- 
tural Philosophy. They have been consi- 
dered as giving the doctrines concerning 
the propagation of sound. Most sounds, 
we all know, are conveyed to us by means 
of the air. In whatever manner they either 
float upon it, or are propelled forward in 
it, certain it is, that, without the vehicle ot 
this or some other fluid, we should have n# 
