ATT 
183 
ATT 
tinct cause, human sagacity has not been 
able to discover. 
l.The attraction of cohesion may be ob- 
served in almost all the common operations 
of nature, and is exemplified by variety of 
easy experiments. Two leaden balls, having 
each a smooth surface, if strongly compress- 
ed together, will cohere almost as strong] \ 
as if united by fusion ; and even two plates 
of glass, if tiie surfaces are even and dry, will 
require some force to separate them. By 
the same law of nature the particles of even 
fluid bodies, in which the attraction is ne 1 
cessarily weaker than in solid substances, in- 
dicate a disposition to unite. 
The drops of dew that appear in the morn- 
ing on the leaves of plants assume a globular 
form, from the mutual attraction between 
the particles of water. Small portions of 
quicksilver, when brought near to each 
other, will run together, and assume the 
same globular appearance. Also, by the 
same law, a vessel may be filled with wa- 
ter, mercury, or any oilier fluid, above the 
brim, and the fluid will be observed to rise in 
a convex form. 
To tliis principle we may very properly 
refer what is termed capillary attrac- 
tion. Thus, if a fluid is contained in a vessel 
not full to the brim, it will always be at- 
tracted to the edges of the vessel, and will 
assume a concave form. Thus, also, if two 
plates of glass, at a small distance from each 
other, are immersed perpendicularly in wa- 
ter, the fluid will rise above its level between 
the two plates, and the height to which it 
rises will bear a certain proportion to the 
distance of the plates, A capillary tube 
is a tube with an exceeding small bore, 
and by the same law which raises the water 
between the plates of glass, a fluid will rise to 
a considerable height in one of these tubes. 
Both these experiments will answer equally 
well in the vacuum of an air-pump, which 
proves that the effect is not owing to the pres- 
sure of the air. In the same manner also, and by 
the same law, fluids will ascend in the cavity 
of a sponge, in the interstices of linen cloth, 
er any porous body. 
2. The attraction of combination, or che- 
mical or elective attraction, is in many re- 
spects analogous to the attraction of cohesion. 
Like the latter, it seems to depend on the 
minute particles of bodies being brought 
nearly into contact with each other ; and in- 
deed so nearly alike are the effects of these two 
species of attraction, that if they are different in 
principle, it is difficult to say which is the most 
essential to' the cohesion and solidity of bo- 
dies. Chemical attraction may probably be 
no other than the attraction of cohesion act- 
ing in a free and unresisting medium, since 
its only distinguishing characteristic is the 
disposition which bodies in solution indicate 
to unite with certain substances in preference 
to others. To make this clear by an experi- 
ment: If silver is added to a quantity of 
aqua fortis, the cohesion of the particles of 
silver will be destroyed, and they will unite 
forcibly with those of the aqua fortis. The 
fluid will however, remain perfectly clear; 
the particles being so extremely minute, that 
the rays of light will suffer no interruption in 
passing through them. If however to this 
solution of silver a quantity of mercury or 
quicksilver is added, the aqua fortis will be 
Vol. L 
: attracted by the mercury, and the silver will 
precipitated, or thrown to the bottom of 
the vessel in which the fluid is contained ; if, 
again copper is added, it will assume the 
place of the quicksilver; and if to this solu- 
tion of copper a bright piece of iron is in- 
troduced, the acid will immediately quit the 
copper, and seize upon the iron, a quantity 
of which being dissolved in the fluid, and the 
copper will be deposited in its place on the 
surface of the bar of iron. The iron may 
afterwards be displaced by the addition of 
an alkali. This species of attraction is call- 
ed combination; because the particles of 
two bodies by those means become so inti- 
mately united or combined, that they can- 
not be separated but by the addition of a 
third body, which has a greater attraction for 
one of the Component bodies than they have 
for one another, and it is called elective at- 
traction and affinity, from the superior tend- 
ency in substances to unite with certain bo- 
dies in preference -to others. In all cases of 
elective attraction it is necessary, that at least 
one of the bodies should be in a fluid 
state. 
3. The attraction of gravitation materially 
differs from the two preceding species of 
attraction, since it requires neither the par- 
ticles of the bodies, nor the bodies them- 
selves, to be brought into immediate contact, 
but acts at considerable distances, and in this 
respect it is analogous to the attraction of 
magnetism and electricity. 
The most obvious effect of gravitation is 
the general tendency of bodies to the surface, 
or perhaps to the centre, of the earth. It 
appears to be one of the great laws of gra- 
vitation, that the attraction of bodies is’ in 
proportion to the quantity of matter they 
contain. The earth, therefore, being such 
an immense aggregate of matter, is sup- 
posed to destroy the effect of this attraction 
between smaller bodies, by forcibly compel- 
ling them to itself. The attraction of moun- 
tains, however, upon the balls of pendulums, 
has been found, by repeated observations, 
to be very considerable. 
The efficient cause of this species of at- 
traction is as much a secret as all the other 
great principles of nature. But first, it ap- 
pears, that the gravitating force being propor- 
tioned always to the quantity of matter, all 
bodies gravitate from equal distances with 
equal velocity, except prevented or impeded 
by some resisting medium. Thus, though a 
guinea and a feather will not fall to the 
ground with equal velocity in the open air, 
because of the resistance of that fluid, yet 
if the air by any means is removed, as in the 
vacuum of an air-pump, they appear to fall 
at the very same instant of time: for though 
the guinea contains considerably more of so- 
lid matter than the feather, and consequently 
requires a more considerable force to put it 
in motion, yet it appears that the attractive 
power being proportioned to the quantity 
of matter, ns velocity is equal to that of a 
body which requires less force to put it in 
motion. 
Secondly, The attractive force of bodies is 
reciprocally as the square of the distances. 
Thus, if a body is of the weight of one hun- 
dred poun Is at the distance of ten diameters 
of the earth, at half that distance it would 
have four times that weight, or the force of 
A a 
A US 
gravity would be exerted upon it in a qua- 
druple ratio, and so in proportion as it ap- 
proaches the body of the earth. 
4. d ire attraction of magnetism onljt/dif- 
fers from that of gravity in its operations 
being limited to particular substances. The 
magnet is an ore of iron, and its property 
of attracting certain portions of that metal 
at moderate distances is well known. Like 
the attraction of gravitation, that of magnet- 
ism bears a proportion to the distance, and 
probably to the quantity of magnetic matter in 
the attracting bodies. But the properties ot 
the magnet are so curious and important in 
nature, that they well deserve a distinct con- 
sideration. 
5. The attraction of electricity is also ana- 
logous to that of gravity in the property of 
acting upon bodies at a certain distance ; 
but it differs from it in its operation being 
confined to a particular state of those bo- 
dies, that Ls, when excited by friction. 
Attraction of mountains* See Moun^ 
tains, 
AVADOUTAS, a sect of Indian bramins, 
distinguished for their austerity and absti- 
nence. 
AVAIL of marriage, in Scotch law, de- 
notes a custom, by which the superior was 
entitled to a certain sum from his vassal, 
upon his attaining the age of puberty. 
AVALANCHES, a name given in Switz- 
erland and Savoy, to those prodigious masses 
of snow, which are precipitated with a noise 
like thunder fronn the mountains, destroy- 
ing every thing in their course. They have 
sometimes overwhelmed whole villages. 
. The best preservative against their effects 
being the forests with which the Alps 
abound, there is scarcely a village situated 
at the foot of a mountain, that is not shelter* 
ed by trees, which the people preserve with 
uncommon reverence. Thus what consti- 
tutes one of the principal beauties of the 
country, affords security also to the inhabit- 
ants. 
A VANIA, in Turkish customs, a fine for 
crimes and on deaths, paid to the governor 
of the place. In cities and towns where se- 
veral nations live together under a Turkish 
governor, he takes this profitable method 
of punishing all crimes among the Christians 
or Jews, unless it be the murder of a Turk. 
AVAST, in the sea language, a term re* 
quiring to stop, to hold, or to stay. 
AVANTUBINE, in natural history, a 
yellowish stone full of sparkles, resembling 
gold, very common in France. An artificial 
imitation of it is made by mixing sparkles of 
copper with glass whilst it is in fusion, which 
is used by enamellers, and to sprinkle, as 
sand, upon writing. 
AUBANE, in the old customs of France, a 
right vested in the sovereign of being heir to 
a foreigner that died within his dominions. 
By this right the French sovereign claimed 
the inheritance of all foreigners that died within 
his dominions, notwithstanding any testament 
the deceased could make. 
AUBIN, in horsemanship, a broken kind 
of gait between an amble and a gallop, ac- 
counted a defect. 
AUBLETIA, in botany, a genus of the 
class and order polyandria monogynia. The 
essential character is, cal. five-leaved ; cor. 
five-petalled ; caps, many-cellcd, echinate, 
with many seeds in each cell. There are 
