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of a powerful mutual repulsion, as is always the case in gaseous bodies, and therefore tend to separate from each other; but as this repulsive force diminishes as the distance of the particles from each other increases, Dr. Wollaston imagined that the weight of the individual particles might come at last to balance it, and thus prevent their further divergence. On this view, which is probable on other grounds, the expansion of a gas, caused by the removal of pressure, will cease at a particular point of rarefaction, and the gas not expanding farther, will come to have an upper surface, like a liquid. The earth's atmosphere has probably an exact limit, and true surface.
It is found by experiment that 480 cubic inches of air at the temperature of 32o expand to 481 cubic inches at 33°, to 482 cubic inches at 34°, and similarly for every successive rise of 1° in the temperature there is an expansion of one cubic inch in the volume, equal increments of the one corresponding with equal increments of the other. This increase of volume is equivalent to a corresponding increase of elastic force, and hence we may say, The elastic force of a gas is increased by increasing its temperature. This, from the name of its discoverer, is called Amonton's law.
The air-pump is a machine for exhausting the air from a vessel termed a receiver, usually made of glass, and ground so as to fit closely to a metallic plate. Its action depends on the expansive power of the air; for in virtue of this property, when any portion of air is withdrawn from the receiver, the remaining quantity immediately dilates and fills the whole space. When a small quantity of air is thus made to fill a large space it is said to be rarefied. If a bell be rung under the exhausted receiver of an air-pump it can scarcely be heard; and hence it is concluded that air is necessary to the propagation of sound. A thermometer placed under a receiver indicates an instantaneous fall in the temperature, if the contained air be rarefied by partial exhaustion. This shows, that in proportion as air is rarefied its capacity for latent heat is increased, and explains the chief cause of the low temperature that prevails on the tops of high mountains, where the air, being under less pressure from the superincumbent atmosphere, is much more rarefied
than in the valleys. At the level of the sea, water boils at 212°, but at a much lower temperature under an exhausted receiver. The same cause operates in mountainous districts, where, from the rarity of the atmosphere, its boiling point is so reduced that it cannot be sufficiently heated to cook certain kinds of food.
The condenser is an instrument by means of which a large quantity of air is forced into a vessel
. In proportion to the condensation the elastic force of the air is increased. This may be carried to almost any extent, as is shown in the air. gun, where, by this means, the elastic force is rendered sufficient to propel a ball with the force of gunpowder. A familiar instance of the force of air under compression is seen in the use of the
pop-gun. From these illustrations it is evident that the elastic force of air is increased both by compression and by heat. This increase conforms to a regular law in the case of all permanently gaseous bodies; but, when vapours are subjected to similar experiments, irregularities are observed that have not hitherto been satisfactorily accounted for.
O day most calm, most bright,
Thy torch doth show the way.
The other days and thou
Till thy release appear.
Man had straight forward gone
The which He doth not fill.
Sundays the pillars are,
Which parts their ranks and orders.
The Sundays of man's life,
More plentiful than hope.
This day my Saviour rose,
Who want herbs for their wound.
The rest of our creation Our great Redeemer did remove With the same shake, which at His passion Did the earth and all things with it move. As Samson bore the doors away, Christ's hands, though nail'd, wrought our salvation,
And did unhinge that day.
The brightness of that day
And fit for Paradise.
Thou art a day of mirth:
Fly hand in hand to heaven !-Herbert.
LESSON XIV. -THURSDAY.
ENGLISH HISTORY-TUDOR LINE, The accession of Elizabeth was hailed with joy by all friends of the Reformation. The daughter of Anne Boleyn, she belonged by birth and education to the Protestant party, and during her sister's reign she had suffered close imprisonment, and had been watched with the most jealous suspicion. Her early policy was distinguished by wisdom and prudence; by a series of firm yet cautious measures the final separation of England from the Romish see was achieved —the Reformed faith established—and the weight of English influence thrown into the scale of freedom and independence.
To avoid the evils of a disputed succession, the queen was urged by Parliament to marry. But her high spirit shrank from admitting any one to a share of her power; she rejected every proposed alliance, and expressed a resolution to lead a life of independence as “a maiden queen.” The next heir to the throne was Mary Stuart, queen of Scotland, who had been brought up at the French court as the wife of Francis II., and at the death of her husband returned to her ancestral dominions. Young - beautiful - an eager Catholic, and in heart a Frenchwoman-Mary was ill fitted to rule a people who had revolted from her faith, and to whose character and habits she was a stranger. By her marriage with Lord Darnley she displeased her subjects; his murder and her subsequent marriage to the murderer, Bothwell, finally alienated them, and she was compelled to abdicate in favour of her son. Escaping across the border, she sought the protection of England, and was detained in captivity, -a violation of national hospitality which it is impossible to justify, but for which the dangers and exigencies of Elizabeth's position plead some excuse ; for she stood alone against a host of enemies, and the princess who had fallen into her hands sought her throne, and the restoration of Popery. From this time, however, the tranquillity of her reign was at an end; successive conspiracies disturbed her peace, and threatened her life. The Catholics in the northern counties, headed by the earls of Northumberland and Westmoreland, raised a formidable though unsuccessful insurrection; the duke of Norfolk engaged in a project to release the
queen of Scots, marry her, and place her on the throne -an attempt which cost him his life. Nor were these schemes confined to the disaffected in England. There is abundant evidence that they were supported by the continental Catholic powers, and formed part of a great plan to crush the Reformation. Meanwhile, the duke of Alva was practising the most revolting cruelties upon the Protestants of Flanders, and the terrible massacre of St. Bartholomew at Paris, whose example was followed in other French towns, roused throughout England a thrill of horror, indignation, and sympathy. Men and money were at once sent to assist the Low Countries in throwing off the yoke of Spain. Sir Francis Drake and other naval captains were countenanced in fitting out private expeditions to plunder Spanish ships, and damage her possessions in the New World; and whilst war and civil strife were desolating the continent, the strength of England was augmenting, and her resources accumulating for future need. A fresh plot, headed by Babington, to assassinate Elizabeth, and deliver the queen of Scots, sealed the fate of that unfortunate captive, whose execution is the darkest stain
the memory of her rival. England was now threatened with a fresh danger, that of