EAR 



EAR 



ed within it. Before this period little 

 was known of the gravity or density of 

 the earth, though the relative densities 

 of that and others of the planets had 

 been ascertained with tolerable preci- 

 sion. From the data thus acquired, the 

 quantity of matter in the earth is known 

 to be equal to the product of its density 

 by its magnitude ; the force of attraction 

 on the surface has been proved by expe- 

 riments, that substances fall 16 1 feet in 

 one second of time ; and hence, that if 

 any place within or beyond it may be 

 known, as in the former case the force is 

 at its distance from the centre, and in the 

 latter as the square of its distance from 

 the same point. 



The earth has three motions : that 

 which gradually occasions the precession 

 of the equinoxes ; that round its axis, 

 which causes the succession of day and 

 night, accomplished in 24 hours ; and that 

 of the whole mass round the sun in a 

 wide orbit, of which the luminary of day 

 is the centre : in the latter its axis is 

 constantly parallel to itself, and inclined 

 in the same angle to its path ; thus pro- 

 ducing the visible and perceptible alte- 

 ration from spring to summer, and from 

 that period to winter. This annual mo- 

 tion of the earth round the sun is per- 

 formed between the orbits of Venus and 

 Mars with the former, and that of Mer- 

 cury within its own, or between it and 

 the sun in the centre, and those of Mars, 

 Jupiter, Saturn, &c. above it or without, 

 which are called from this circumstance 

 superior planets, and the rest inferior. 

 The time occupied in performing this re- 

 volution is 365 days, 6 hours, and 49 mi- 

 nutes, or a tropical year, calculated from 

 an equinox or solstice to the same again ; 

 the sideral year, as computed from any 

 iixed star to the same point, and seen 

 1'rom the sun, makes the revolving of the 

 earth to occupy 365 days, 6 hours, and 

 9 minutes : the figure of the orbit is el- 

 liptical, with the sun in one focus: the 

 supposed distance is 95 millions of miles, 

 adaiitting the sun's parallax to be BSf' t or 

 the angle beneath which the semidiame- 

 ter of the earth would appear from the 

 sun ; " and the eccentricity of the orbit, 

 or distance of the sun in the focus from 

 the centre of this elliptic orbit, is about 

 jfo of the mean distance." 



There are nine descriptions of earth, 

 which are, barytes, strontian, lime, mag- 

 nesia, alumina, yttria, glucina, zirconia, 

 and silica. Every substance is an earth 

 which is insoluble in water, or becomes 



so when combined with carbonic acid, j 

 with little taste or scent under the above ; 

 circumstances, and incapable of altera- 

 tion by fire when in a pure state, then 

 capable of being turned to white pow- 

 der, and not exceeding 4.9 in specific 

 gravity. 



The word earth is generally applied to 

 the whole mass of the globe, and always 

 to the mould which supports the growth 

 of vegetables ; the latter has been atten- 

 tively examined by various chemists, and 

 found to consist of several substances, 

 without any regularity in their arrange- 

 ment. 



EARTHQUAKE. The dreadful conse- 

 quences attending sudden and violent 

 tremblings of the earth, are sufficient 

 reasons tor attempting toaccount for their 

 causes, but, as from the nature of those 

 it is utterly impossible to ascertain them 

 accurately, rational conjecture must be 

 accepted in place of actual observation. 

 Every writer on the effects of volcanic " 

 eruptions concurs in attributing earth- 

 quakes to their internal operations, which 

 become less frequent in their neighbour- 

 hood after violent explosions through the 

 craters ; indeed, it must be obvious on 

 the first thought, that the furious ef- 

 forts of fire, hot air, and steam, exclu- 

 sive of electric matter, cannot but pro- 

 duce convulsive motion in the substances 

 which confine them, and of more or less 

 extent and violence, in proportion to 

 the cause. When a free passage is ob- 

 tained, the agitation gradually subsides, 

 and is only increased at intervals by the 

 escape of accumulated matter. Sir Wil- 

 liam Hamilton, who carefully examined 

 all the visible phenomena produced by 

 the earthquakes of 1783, in Calabria, is de- 

 cidedly of opinion that they originated 

 from under the sea, situated between the 

 coast of Calabria and the island of Strom- 

 boli, or near the city of Oppida, which he 

 illustrates, by forming a circle round those 

 points, and remarking that the most de- 

 structive effects were there, whence they 

 became gradually less ruinous. Mount 

 Stromboh had been unusually quiet for 

 some time previous to this calamitous pe- 

 riod, a circumstance highly favourable to 

 his conjecture, founded besides on the 

 experience of remote ages, when, ac- 

 cording to Strabo, Campania was sub- 

 ject to frequent and dreadful earth- 

 quakes, which were less common and 

 ruinous after Vesuvius had become the 

 means of dispersing the confined mat- 

 ter. Since that fortunate zera, the vicini- 

 ty of the above mountain has suffered 



