Chap. XI.

MECHANICS.

915

Riga

Eng. grs.

Eng. grs.

- 6149

Vicenza

-

- 6879*

Rome = 12 oncie

- 5257-

Vienna , commercial

- 8648*

oncia = 8 drainme.

apothecaries 420- Fr. gram.

dramma = 3 scrupoli.

mint mark 280-64 Fr. gram.

scrupolo= 12 oboli.

carat of the jewellers *206085

obolo = 4 silique.siliqua =12 grani.

Fr.

gram.

Rouen -

- 7772-

djwthecaries'

Grains

of different Countries

Saragossa

- 4707 •

from

Vega .

Scotland troy pound Dutch

- 7621-8

.Austria

-

- 1*125

iron pound, £ troy

- 9527*25

Bern

-

*956

Seville, see Cadiz .

France

*981

Smyrna, commercial pound

6544-

Genoa

_

*850

Stettin -Stockholm

- 6782*

- 9211-

Germany -

-

f *958* L *959

Strasburg

- 7277*

Hanover

-

*978

Toulouse

- 6323-

Holland

-

•989

Turin -

- 4940-

Naples

_

-860

Tunis -

- 7140*

Piedmont -

.

■824

Tyrol ...

- 8693*

Portugal

-

*864

f 4215-

Koine

-

•909

Venice ...

- j 6827-

Spain

-

•925

(,5374-

Sweden

-

- . *955

Verona ...

- 4676-

Venice

-

•809

CHAP. XL

MECHANICS.

As quantity, space, and number are understood and comprised in mathematics, so theirapplication more immediately belongs to mechanics and hydrodynamics: but before weenter into the principles which affect falling bodies or those which belong to bodies re-volving round a centre, or the general laws of machinery, it is necessary to describe thephysical properties, or those external signs by which matter is recognised either in its solid,liquid, or aeriform condition.

Extension is that property by which a body occupies a certain space: by it is understoodits volume or figure ; the measure of the extension and compression of uniform elasticbodies is proportionable to the force which produces it; when, for instance, a weight issuspended to a bar of iron, causing it to be prolonged, if twice that weight be added, theeffect will be doubled, and it was proved by Dr. Ilooke, that the application of theseweights in a contrary direction would shorten the bar in the same proportion. Dr. Younghas suggested that the elasticity of a substance may be expressed by the weight of a certaincolumn of the same substance, which he calls the modulus of elasticity, and of which theweight is such that any addition to it would increase it in the same proportion as the weightadded would shorten by its pressure a portion of the substance of equal diameter.

Impenetrability implies that a body is so compact in its structure as not to allow anotherto pass through it.

Matter may be understood to comprehend whatever occupies space, and possesses ex-tension and impenetrability ; such are all bodies that have magnitude, or that compriselength, breadth, and thickness, as well as those which have surfaces only.

Porosity is that property which indicates that there are interstitial spaces lying betweenthe particles or molecules of matter, usually called pores.

Mass and Density are estimated according to their various properties of porosity ; themass comprises the material particles, and the greater their quantity the less porous thebody or substance will be: density, on the other hand, expresses the relation of the masseswhen the volumes are equal; or, of any two bodies, that is the most dense which with equalbulk contains the greater mass.

Coinpressibility implies that the body may be diminished by pressure without the massbeing lessened by forcing the particles which compose it closer together and diminishingthe size of the pores.

Dilatability is the reverse of the former : the pores are increased by throwing the particlesfarther from each other, which is affected by heat, or raising the temperature of a body.

Elasticity is the power of a body to resume its original state, as in the case of a spring,or when compression has taken place.

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