580 
EAR 
more amt more towards the east, other stars 
seem to rise and advance westwards, passing 
tae meridian ot the observer, when they are 
due south from him, and at their greatest 
altitude above his horizon ; after which, by a 
continuance of the same motions, viz. of the 
earth’s rotation eastwards, and the luminaries’ 
apparent counter-motion westwards, these 
decline from the meridian, or south point, 
towards tire west, where being arrived, they 
are said to set and descend below it ; and so 
on continually from day to day ; thus making 
it ciav while the sun is above the horizon, and 
night while he is below it. 
. .While the earth is thus turning on its axis, 
h is, at the same time, carried by its proper 
motion in its orbit round the sun, as one of 
the planets ; namely, between the orbits of 
\ enus and Mars: having the orbits of Venus 
and Mercury within its own, or between it 
and the sun, in the centre, an$ those of Mars, 
Jupiter, Saturn, c Scc. without or above it; 
which are, therefore, called superior planets, 
and the others, interior ones. This is 
caded the annual motion of the earth, because 
it is performed in a year, or 365 days 6 hours 
nearly ; or rather 365 days, 5 hours, and 40 
minutes, from any equinox or solstice to the 
same again, making the tropical year; but 
Irom any fixed star to the same again, as seen 
from the sun, in 365 days, 6 hours, 9 minutes, 
which is called the sidereal year. The figure 
of this orbit is elliptical, having the sun in 
one focus, the mean distance being about 95 
millions of miles ; which is upon the suppo- 
sition that the sun’s parallax is about 8 "1, 
or the angle under which the earth’s seim- 
diafneter would appear to an observer placed 
in tiie sun ; and the eccentricity of tiie orbit, 
or distance of the sun, in the focus, from the 
centre of tiiis elliptic orbit, is about _t_th of 
the 'mean distance. 
EARTHS. The word earth, in common 
language, has two meanings : it sometimes 
signifies, as we have seen, the globe which 
•we inhabit, and sometimes the mould on 
which vegetables grow-. Chemists have ex- 
amined. this mould* and have found tiiat it 
consists of a variety of substances mixed 
together, without order or regularity. The 
greatest part of it, however, as well as of the 
stones which form apparently so large a 
proportion of the globe, consist of a small 
number of bodies, which have a variety of 
common properties. These bodies chemists 
have agreed to class together, and to deno- 
sunate earths. 
Every body which possesses the following 
properties is an earth. 
1. Insoluble in water, or nearly so; or at 
least becoming insoluble when combined with 
carbonic acid. 2. Little or no taste or smell ; 
at least when combined with carbonic acid. 
3. Fixed, incombustible, and incapable while 
pure of being altered by the fire. 4. A 
specific gravity not exceeding 4,9. 5. AY hen 
pure, capable of assuming the form of a white 
powder. 6, Not altered when heated with 
combustibles. 
The earths at present known, are nine in 
number, namely, 
1. Barytes. 6. Yttria. 
2. Strontian. 7. Glucina. 
3. Lane. 8. Zirconia. 
4. Magnesia. 9. Silica. 
5. Alumina 
Yt Licit. see under their respective names. 
% A R 
Every one of the above characteristics is 
not, perhaps, rigorously applicable to each 
of these bodies; but all of them possess a 
sufficient number of common properties to 
render it useful to arrange them under one 
class. 
Earth Nuts, or Ground Ants. See 
Arachis. 
EARTHQUAKES. When we consider 
the very formidable nature of these pheno- 
mena, we cannot wonder that human inge- 
nuity has been often exercised in accounting 
tor their causes. To explain the theory of 
earthquakes, it will be necessary to recal to 
the reader’s attention what was said in 
the preceding article on the structure of the 
earth, which, being formed of different strata, 
we compared to the leaves of a book or the 
coats of ah onion; and if with this considera- 
tion we combine the operation of subterra- 
neous tires, we shall have at least a probable 
explanation of the cause of earthquakes. 
d’lie sudden explosions which take place 
from volcanoes, probably depend on the ac- 
cess of a quantity of water, which enters 
through some fissure communicating with 
the sea, or which is derived from other 
sources in the earth. If this mass of water 
is sufficiently great, it will extinguish the 
volcano; if not, it will be converted into 
steam, the expansive force of which far ex- 
ceeds that of gunpowder. The elastic fluid 
thus formed either finds vent at the mouth o; 
tiie volcano, or, if the superincumbent weight 
should be too great, it will force a passage 
between the strata of the earth, and occasion 
that undulatory, but sometimes violent, mo- 
tion, which i called an earthquake. From 
various facts demonstrative of the cohesion 
and elasticity of bodies, we are warranted in 
concluding, that the different strata of which 
the earth is composed w ill adhere together, 
and that a freer passage will be afforded to 
any intervening body between the strata than 
directly through them. If the confined fire 
or steam acts directly under a province or 
town, it will heave the earth perpendicularly 
upwards, and the shocks will be more sudden 
and violent. If it acts at a distance, it will 
raise that tract obliquely; and the motion 
will be more oblique, undulatory, and tre- 
mulous. 
The great earthquake at Lisbon, in 1755, 
was felt as far as Scotland ; and from the phe- 
nomena which attended it, it was evident, that 
the ground had a waving motion from south 
to north. All the oblong lakes that lay from 
north to south were much agitated, the wave 
commencing at the south end ; whilst all 
other lakes which lay across, from east to 
west, were much less affected. 
The great distance to which earthquakes 
extend, depends on the compressibility and 
elasticity of the earth; which may be under- 
stood from the vibration of the wails of 
houses, occasioned by the passing of car- 
riages in the adjacent streets. Another in- 
stance is the vibration of steeples by the ring- 
ing of bells or gusts of wind. The Eddi- 
stone lighthouse often vibrates from the force 
of the waves which beat against its founda- 
tion. 
Previous to an eruption of Vesuvius, the 
earth always tremble's, and subterraneous ex- 
E A Im- 
plosion; are heard. On the 1st of November 
1755, the era so fatal to Lisbon, the island: 
of Madeira was violently shaken bv an earth- 
quake, accompanied with subterraneous ex- 
plosions. So thoroughly convinced, indeed, 
are the inhabitants ot volcanic countries, of 
the connection between earthquakes and vol- 
canoes, that when a great eruption takes 
p'ace from a volcano, they congratulate 
themselves on having escaped an earth- 
quake. 
Earthquakes, as well as volcanic eruptions, 
are always preceded by a violent agitation < f 
the sea. Previous to’ the breaking out of 
Aesuvius, the sea retires from the' adjacent 
shores till tiie mountain is burst open, and. 
then if returns with such impetuosity as to* 
overflow 7 its usual boundary. About an hour 
alter the first shocks, which alarmed the city 
ot Lisbon in 1755 the sea was observe < to 
come rushing towards the citv like a torrent, 
though against buffi wind and tide: it rose 
forty feet higher than was ever known, and 
as suddenly subsi le x A ship, fifty leagues 
oil at sea, received so violent a" shock as 
gieatly to injure Uic deck, &c. The same 
effect was observed at Cadiz, and at a mini, 
ber of ports throughout the Mediterranean j. 
and, indeed, more or less, all over Europe, 
That earthquakes are the effect of steam 
generated within the bowels of the earth, and 
tnut they are produced in the manner which 
has been described, appears hig ,iy probable 
trom the quantities of boiling water which 
have occasionally been thrown up by volca- 
noes in different parts of the world. "In 163} 
and 169S, -vast torrents of boiling water Row- 
ed from the crater of Vesuvius, previous to- 
the ei option ot lire; and what was, perhaps, 
slid more rc markablt£ many species of sea- 
slieilq in a calcined state, were found 011 tiie 
Inink of the crater, and also in the channel 
formed by the flood. The same thing hap- 
pened at A.tna, in 1755, when a dreadful 
torrent of boiling water flowed from the era- 
ter at the time of an eruption of lire. Sir 
AY liliam Hamilton observe, that the sea- 
shells emitted along with the water clearly 
indicate a communication with the sea. All 
warm springs probably receive their heat 
from tiie action ot pyrites, near which the 
-water passes. 
Authors of very high repute have, how- 
ever, attributed earthquakes entirely to the 
agency of the electric fluid, and regarded 
them chiefly as violent shocks of electricity, 
\t e must confess there is indeed an intimate, 
though hitherto inexplicable, connection be- 
tween earthquakes and even volcanoes, and 
the electric fluid ; and the state of the atmo- 
sphere previous either to an earthquake or a 
volcanic eruption is always highly electrical. 
1 hough there is hardly any country known 
in which shocks of an earthquake have not 
at some time or other been felt, yet there 
are some much more subject to them than, 
others. It h is been observed, that northern 
countries in general are less subject to earth- 
quakes than, those situated near the equator, 
or in the southern latitudes ; but this does 
not hold universady. Islands are also more 
subject to earthquakes than continents ; but 
neither does this Hold without exceptions.' 
Some particular parts of continents, and 
some particular islands, are more subject to. 
them than others lying in the neighbourhood, 
and differing verv little from them in exter- 
nal appearance. Thus, Portugal is more sub-, 
jeet to earthquakes than Spain, and the. lattes 
