then,” said the rebel, “and a corner-stone I will be. I stand on my rights: all stones are equal; so, quick!—let me occupy a position in the corner.”

“That you cannot do, my friend,” returned the mason: “don’t you see that the corner-stones are already in their places?”

“I see that well enough,” said the Stone; “but you can take one of them out, and install me in its place. I have as clear a right to be there as any of them: equality is the badge of us all: every one of us is from a common quarry: we are all stones alike. Take one of them out, and put me in.”

“Now, see how grossly inconsistent you are!” urged the workman: “all stones, you assert, are equal, and have the same rights: yet you would have me rudely displace and degrade one of them for your pleasure, though, according to your own acknowledgment, you are not a bit better than he is! Upon my word, but you have enlightened conceptions of what constitutes equality. But I cannot stand here arguing the question with you all day; my time is precious; I beg you will decide whether you are satisfied to form part of the wall or not.”

“Assuredly I am,” said the other, “but only as a corner stone. How can you be so blind as not to see that we are all stones alike, and all therefore equal?”

“You are all stones alike,” replied the mason, “and so far equal, in a certain sense; but your equality consists merely in your being all liable to serve as wall-stones, not in your being all qualified for the place of corner-stones.”

“A truce with your slavish doctrines!” cried the malcontent; “either make of me a corner-stone, or build your wall without me.”

“Is that your final decision?” asked the mason. “I warn you not to trifle with me, for I cannot let my work wait for you any longer.”

“I have said it,” said the Stone. “I would see your wall trampled into dust, and the whole universe along with it, before I would surrender my great principle. Do what you please.”

“Go, then, refractory wronghead,” exclaimed the mason, “go and enjoy your equality where none will be likely to dispute it!” And so saying, he cast the Stone from him with a vigorous jerk; and the Stone, after it had completed its journey through the air, fell down, and from the force of its own gravitation sank several feet low into the bottom of a deep and slimy pool.

This was, for all historical purposes, the termination of its existence. What became of it in the pool ultimately, it is impossible to conjecture, for half a century has elapsed since; but as a total extinguisher was put upon its aspirations after notoriety by the accident, it is highly probable that if not worn quite away by the friction of the surrounding mud and water, it was at least gnawed to the core, in a moral sense, by its regrets for the folly of its past misconduct—regrets which we may suppose to have been shared in a pretty equal degree by its twin-brother of the preceding year, which had stickled so stoutly in its colloquy with the mason for its favourite theory of liberty and independence.

THE AIR WE BREATHE.

The objects which come every day before our eyes, the offices which involuntarily and almost unconsciously we at each moment must perform in order that we may live, are precisely the subjects concerning which the mass of mankind are least curious, and of the true nature and utility of which they are the most completely ignorant. It is thus with the air we breathe. There is no person but is aware of the necessity of breathing, and of the motion of the air caused by winds; but how few have asked themselves, What is air? How much is there of it? Could the same air be always used for breathing? How do fishes manage living in water in place of air? Yet the information thus obtainable might be the means of saving the lives of hundreds, as certainly the ignorance on these points has been the source of death, by painful and lingering torture, in many cases. We purpose, therefore, now to give some information about air, to show the importance of it to mankind, and to indicate how much we owe to the Omniscient Providence that has given to air the properties that we find it to possess.

Although “trifles light as air” has become a proverb, yet air is positively heavy. A hogshead of air weighs about ten ounces; this is heavier than the gas which is burned in the streets and shops, of which a hogshead would weigh only seven ounces; and very much heavier than hydrogen gas, with which balloons were formerly filled, a hogshead of hydrogen gas weighing only two-thirds of an ounce. A balloon filled with hydrogen, or even with coal gas, rises into the air, as oil or a cork rises up through water. The air being thus heavy, presses upon the earth; and by measuring the degree of pressure we can tell how much air there is. This is done by an instrument termed a barometer—a glass tube closed at one end, and which, having been filled with quicksilver, is turned upside down in a cup containing quicksilver also. The tube being shut at the top, the air does not press on the quicksilver inside, but presses upon that in the basin; the quicksilver in the tube, which tends naturally to fall down into the basin, is thus forced to remain up in the tube by the pressure of external air; and it rises so high that the pressure inside, of the quicksilver, and outside, of the air, is equal. If the pressure of the air diminishes, the quicksilver falls; if the pressure of the air increases, the quicksilver rises: and as all great changes of the air are connected with changes of the weather, the barometer is generally known and consulted as a sort of weather-glass.

Every space of an inch square supports fifteen pounds weight of air; at the rate of ten ounces to a hogshead, the depth of the air would therefore be about five miles. But it is much deeper, for air is what is termed compressible—that is to say, it may by pressure be squeezed into a smaller bulk; and hence the air next the ground, being compressed by the portions above it, is much the heaviest portion. At three miles high a hogshead of air weighs only five ounces, and at eight miles high only two ounces; hence the limits of the air are much farther removed, and it is known to extend to at least forty miles.

The office of the air is to support animal life: no animal can live without air: even fishes require air. The water in which they swim contains air mixed with it, and this water washing the gills, which are their lungs, serves to them as the air directly acts on us. If we boil water until the air is expelled from it, and let it cool in a close vessel, we may drown a fish by putting it into such water, as easily as a land animal; it could not breathe. It is thus that in the lakes on the tops of very high mountains there are no fish. The heights are deserted by land and by water animals, in consequence of the air being too thin to support life. The way in which the air acts upon the body is very interesting. The most abundant element of our food is what the chemists term carbon, of which, in a gross manner, charcoal may serve as an example. Now, we eat much more of this than we require for the supply of our bodies, and it must be got rid of. This is done by its uniting in the body with a substance termed oxygen, and forming carbonic acid, the sort of air which boils up in soda water and ginger beer. This dissolves in the blood, colouring it a deep purple, and escapes from it when by the action of the heart the black blood is exposed to the action of the air on the surface of the lungs. Now, the office of the air is to supply this oxygen which removes the carbon from the blood. But the air is not pure oxygen. If it were, it would act too violently. An animal which breathes pure oxygen, becomes flushed, pants violently, and, if not choked, dies of inflammation of the lungs, produced by the intense action. In the