ACT 
and suddenly contracting near the tail, 
which is short and slightly acuminate. A. 
dubius, which very nearly resembles the 
javanicus, except that the head is covered 
with very minute, rough, and warted scales, 
differing in size alone from those on the 
other part of the animal. The dubius mea- 
sures only about three feet in length. A 
specimen is to be seen in the British Mu- 
seum. Its native place is not ascertained. 
A. fasciatus, resembles the dubius so much, 
that some naturalists suppose them both to 
be of the same species, and differing only 
in age and cast of colours. The specimen 
in the British Museum is about eighteen 
inches long. See plate Serpentes, fig. 1. 
ACRONICHAL, or Achronycal, in 
z astronomy, an appellation given to the ris- 
ing of a star above the horizon, at sunset ; 
or to its setting, when the sun rises. Acro- 
nichal is one of the three poetical risings of 
a star ; the other two being called cosmical 
and helical. 
This term is also applied to the superior 
planets Saturn, Jupiter, and Mars, when 
they are come to the meridian of midnight. 
ACROSTERMUM, in botany, a genus 
of the Cryptogamia Fungi class and order ; 
fungus quite simple, nearly erect, emitting 
the seeds exteriorly from the top. There 
are four species. 
ACROSTICUM, rusty-back, wall-rue, or 
forked-fern, in botany, a genus of ,the Cryp- 
togamia Filices ; the character of which is, 
that the fructifications cover the whole in- 
ferior surface of the leaf. There are 45 
species distributed into different classes. 
Few of the species have been introduced 
into gardens. Those of Europe may be 
preserved in pots, filled with gravel and 
lime-rubbish, or planted on walls, and arti- 
ficial rocks; but most of them being natives 
of very hot climates, must be planted in 
pots, and plunged into the bark pit. 
ACTZEA, in botany, a genus of plants of 
the Polyandria Monogynia class and order. 
Gen. character ; calyx perianth, four-leaved ; 
leaflets roundish, obtuse, concave, cadu- 
cous ; cor. petals four, accumulate to both 
ends, larger than the calyx ; filaments about 
30 ; germ superior ovate ; no stile ; stigma 
thickish, obliquely depressed; pericarp a 
berry, oval-globose, smooth, one-furrowed, 
one celled ; seeds very many, semi-orbicular, 
lying over each other in two rows. There are 
four species, viz. thespicata; racemosa; ja- 
ponica, and aspera ; of the first there are 
varieties, as the black-berried herb Christo- 
pher, or bane-berry, found in the northern 
ACT 
parts Of England; the Christopher with 
white berrries, a native of America; and 
that with red berries. The racemosa, or 
black snake-root, found also in America, of 
which the root is much used in many disor- 
ders, and is supposed to be an antidote 
against the bite of the rattle-snake. The 
leaves of the A. aspera, being extremely 
rough, the Chinese use them in polishing 
their tin ware. 
ACTINIA, in natural history, a genus of 
the Mollusca order of worms ; the charac- 
ters of which are, body oblong, cylindrical, 
fleshy, contractile, fixed by the base ; mouth 
terminal, expansile, surrounded with nu- 
merous cirri, and without any aperture. 
There are 36 .species. These marine ani- 
mals are viviparous, and have no aperture 
but the mouth. They feed on shell-fish, 
and other marine annuals, which they draw 
in with their feelers, in a short time reject- 
ing through tire same aperture the shells 
and indigestible parts. They assume various 
forms ; and where the tentacula or feelers 
are all expanded, have the appearance of 
full-blown flowers. Many of them are eat- 
able, and some of them very sapid. 
ACTINOLITE, in mineralogy, a family, 
comprehending six species, viz. the actino- 
lite, smaragdite, tremolite, cyanite, saylite, 
and schalstone. The actinolite occurs 
chiefly in beds in primitive mountains, and is 
divided into three sub-species, viz. the as- 
bestos, common, and glassy. The asbestos 
colours greenish grey, mountain green, 
smelt blue, olive green, yellowish, and liver- 
brown, Massive, and in capillary crystals. 
Soft; brittle; specific gravity 2.5 to 2.9. 
Melts before the blow pipe. The usual co- 
lour of the common is leek green, but its 
specific gravity is between 3,0 and 3.3. 
The principal colour of the glassy is moun- 
tain green, passing to the einerald green. 
Specific gravity 2.9 to 3.9. 
ACTION, in mechanics and physics, is 
the pressure or percussion of one body 
against another. 
It is one of the laws of nature, that 
action and re-action are equal, that is, 
the resistance of the body moved is always 
equal to the force communicated to it ; or, 
which is the same thing, the moving body 
loses as much of its force, as it communi- 
cates to the body moved. 
If a body be urged by equal and contrary 
actions or pressures, it will remain at rest. 
But if one of these pressures be greater than 
its opposite, motion will ensue toward the 
parts least pressed. 
