ESSAYS MORAL AND LITERARY. No. 3.-On Retrospection. "The present joys of life we doubly taste, When looking back with pleasure on the past." That man may be said to live long, who is often engaged in looking back upon the past; for the proper estimate of life, does not depend upon months and years, but upon the events which have happened to us since we had a being. Actions, not the revolution of PERFECT happiness is not the lot of the seasons, are what we have to judge humanity; we are born for trouble as by. That individual who has most to the sparks fly upward. But perhaps treasure up, and who contemplates the mixture of good and evil fate which the oftenest, partakes most of exisis given to every man, ought not to be tence, whether his life be thirty, or made the cause of so much regret as threescore years and ten. To mere it frequently is. We know that our listless sensation, one day is as a enjoyments are increased by the endu- thousand. But it is also the faculty rance of previous sorrows; and that of the mind not only to observe these the cup of consolation which we occurrences which belong to itself, but sometimes taste, is the sweeter from in imagination at least to become the remembrance that there have been acquainted with what has befallen times when it was not ours. A long others; to learn what has been the series of unbroken misery, is almost fate of kings and conquerors, of phiimpossible to exist; and the few sun-losophers and statesmen; and to recur ny spots that light up the track of human life, are dearer to us from the consciousness that they have been but few. It is the many turns in our eventful journey-the joys and griefs which have been given to us, that make life so dear, and that cause it to be a fit subject for meditation. Perhaps there is not a purer pleasure in which we can be engaged, than in dwelling upon the varied scenes of our past being, and in considering those conclusions which the calm remembrance of them must voluntarily make. The mind sees where it did right, and where it did wrong; when it was happy, and when it was miserable. We behold the hills and the valleys, the flowers and the brambles, which have crossed our path; we remember the springs of pure water which have flowed by the way-side, and the sweet resting-places where we have reposed, after the day of toil. We recollect some tender trial of feeling, some series of joys, that then seemed wedded for ever-the golden hopes of our youth rise up before us in their dreamlike beauty, and then "come back upon our hearts again," to soothe us with their earliest sympathy. Oh! what a compound is human life!-of what hopes, and loves, and joys, and friendships,-of what griefs, and cares, and broken plensures, is it composed! To begin a review of our past life, is to create for ourselves one of the purest enjoyments; and at the close of our reflections, to become not only wiser but better. to scenes which are as old as the earth on which we tread. It is the great privilege of a meditative man, that let him be situated as he may, be will always find sufficient variety in his own recollections, well to employ his thoughts. He can never be said to be alone, for he has companions in his own bosom, that will never leave him nor forsake him; and he can often walk in the midst of crowded cities with as much composure, as he can in the green fields around his country cottage. He may observe the complex machinery of the universe, he may analyze the passions and motives by which men are actuated, shunning the evil and cherishing the good. He may ramble among the flowers of the valley, and find improvement there; he may watch the rising and the setting sun, and gaze upon the innumerable company of stars, which, "Ebb in the aërial dome, Moving the pendulum of heav'n ;" or turn his thoughts inward, and meditate upon the final destiny of his own being. To such a man time cannot be said to be short; every past hour brings to him something for reflection, and every object he sees, something for instruction; the smallest incident will often awaken him to a remembrance of some considerable occurrence in his life, that passes before him, and that "bears a glass which shows him many more." Perhaps the purest of all our recol lections, or at least that which brings with it the greatest degree of self-satisfaction, is the level days of our childhood. Almost all that we have done, or said, or thought of, since that happy time, has had something of care mixed with it, that has too often sullied and broken our best enjoyments. We feel that when the poet says "the world is too much with us," he is telling us a sorrowful truth, and we are at times ready to determine it shall be so no longer. But its specious gaieties lead us on and on, promising those things they never perform, and holding for our acceptance some faroff good, which we find, too late, is unattainable. Still, amidst all our disappointments, the remembrance of our early days casts a beautiful halo around our path, and throws many a sunbeam on the cloudy skies. Men perhaps are never so decidedly acquainted with what they are and have been, as when overtaken by misfortune, and never feel the real value and pleasure of retrospection so forcibly, as when in this situation. When the heart is searching after some blessing, real or imaginary, it often forgets those joys that are past; and it is only when our expectations receive a gentle check, that we see the full brightness of our early days. It is then that we inwardly wish for another revolution of their artless sports. Childhood is the "glory and the freshness of a dream," which we exchange for "the light of common day ;" and notwithstanding all that we may possess in the world, its power, honour, and riches, there are moments, and not a few, when we are compelled almost involuntarily to exclaim, that there hath passed away a glory from the earth." 66 Next to the pleasure derived from a contemplation of the scenes of our childhood, is that of remembering the hopes and loves of our youth. The one is a season of unalloyed happiness; the other is a state of fear and joy. In the one we follow the innocent dictates of nature; in the other we begin to plan out schemes, and seek to become men of power and affluence. Youth is the time when the mind is formed, and the affections exercised; and in after-years we well remember this period as it gave the bias to our fate. In many cases it may be seen how small an incident No. 42.-VOL. IV. will change the current of life, and how often it is that a mere saying or thoughtless action will decide the destiny of our future days. But there are some men who can scarcely be said ever to have marked out for themselves one decided path; such a man was Rousseau--impatient, romantic, and tender-hearted, he was rather the sport of chance or fortune, than one who travelled in any beaten track. Never was there a man who so intensely remembered his youthful days, and never perhaps was there a man who had so many things to remember. What to me constitutes the chief delight in reading Rousseau's Confessions, is, the vividness with which he pictures his happy moments, and the charm of gentle pity which he casts over his weightiest sorrows. Who can have forgotten his meeting with Madame Warrens, the passionate love he bore for her, which seemed to cling to him with firmer hold as his years increased; or the thrilling exclamations of his withered spirit, which sound upon the ear like those piercing words of Lear, when, amid the desolation of his heart he cried, 'Never, never, never." Perhaps the remembrance of happiness can only be pleasurable when the heart is in some degree peaceful; when it is broken by sorrow, its reflections must be painful. The fittest state for recollection is, when we have partaken of folly sufficiently to know its bitterness, and tasted as much of unbroken joy as to feel its worth. Much more might be advanced, but I shall not proceed;-these few imperfect reflections have been suggested by finding among my papers the following lines. I am not an unhappy man, nor one whose mind is soured by disappointment; yet I cannot help wishing that I was now the same as when I penned these verses, for although nineteen summers have hardly passed over my head, there are few who have tasted more of good and evil life. August, 1820. Well-Childhood's hours are past away, And yet I grieve not-for the time For memory to dwell upon. O'er many a field and woodland far, In scenes where want and sorrow are. The past, a hallow'd track of beauty, And when I think, I'll think of bliss, Let Fancy rest, on that which is Like Hope upon her anchor leaning. A plant whose bloom to earth is given, CHEMICAL ESSAYS.-ESSAY IV. (Continued from col. 516.) In my brief essay on Oxygen, I observed that the blood is converted into a red oxyde, by the oxygen of the atmosphere acting upon the iron contained in the blood; but I should have mentioned also, that there are many modern chemists who deny the existence of iron in the globules of the blood; notwithstanding which, I am still of opinion that the globules of the blood do contain a small quantity of iron; the traces of which I have always found sufficiently distinct to satisfy myself as to the reality of its existence. The oxygen of the atmosphere cannot enter into chemical combination with the carbon thrown off by the blood, to constitute Carbonic Acid Gas, without a portion of caloric being evolved; now this caloric is seized by the arterial blood, and when it passes on to the veins, its capacity for caloric is diminished as much as it had been increased in the lungs; the caloric, therefore, is gradually evolved in the course of the circulation through the minute vessels over the whole body, giving stimulus to the operations of the animal economy, and a beautiful provision for the maintenance of a uniform animal temperature. The blood, then, in passing through the lungs, is freed of two noxious principles, namely, carbon and hydrogen; and indeed the extreme great quantity of the former of these is astonishing, amounting to no less than 11 ounces in the 24 hours. A small quantity of oxygen is absorbed; and the arterial blood becomes loaded with caloric. The support which atmospheric air administers to combustion, entirely depends upon the presence of Oxygen Gas; for combustion will never take place without this gas be present. The atmospheric air is decomposed; the combustible body absorbs its oxygen; while its other constituent parts are set at liberty. Air is invisible, colourless, and elastic, capable of indefinite expansion and compression. Elasticity is one of the most obvious properties of air, and it is, perhaps, the one upon which philosophers have made the greatest number of experiments. We are acquainted with a great number of facts, illustrative of the air contracting its volume, and recovering the state from whence it was displaced, upon the entire removal of the causes by which it was compressed. If a bladder, containing a small quantity of air, be tied up with a string fast round its neck, and placed under the receiver of an air pump, it will gradually swell as the receiver is exhausted, till it becomes quite full, which is owing to the elasticity of the small quantity of air contained in the bladder, dilating and expanding itself on the removal of the atmospheric pressure. The same expansion takes place if we carry the bladder to the top of a very high mountain. So likewise bubbles of air rising from the bottom of a glass of water, gradually dilate as they approach towards its surface, owing to the gradual diminution of the pressure of the water. It is also owing to the elasticity of the air, that thin glass globes filled with air burst asunder upon the exhaustion of the receiver of an air pump. The generality of fishes are furnished with an air bladder; which is placed very near to the backbone; 1 and this they have the power of contracting and dilating at pleasure. By contracting this bladder, and thereby condensing the air within it, they can, with very little exertion, render themselves specifically heavier than water, and enable themselves to sink to the bottom. On dissection of the bladder of fishes, we find that it has an extremely strong muscular coat, by means of which the animal has the power of contracting and dilating its bladder to a smaller or greater size as best suits its convenience; and thereby of swimming in any depth of water, or rising to the surface with the greatest facility. It is upon this property of the air of which we have been speaking, and upon which we shall make some further observations, that the forcing pump and air-gun are constructed; and it is also by this property that air is chiefly distinguished from other fluids. It is the generally received opinion, that the atmospheric air owes its elasticity entirely to the caloric it contains. As a proof of the great elasticity of the air, it will be sufficient to observe, that Mr. Boyle succeeded in dilating it, till it occupied nearly 14,000 times its ordinary space, without the application of heat, and by only removing the pressure by means of an air-pump. The elasticity of the air is diminished by cold, and greatly increased by the application of heat, as may be shewn by holding a bladder, containing a very small quantity of air, to the fire; upon the rarefaction of the inclosed air, it will gradually expand till it appears quite plump, and will return to its former flaccid state, when reduced to its former temperature. It is upon this principle that the structure and use of the thermometer depends. The next property of the air which I shall notice, is its fluidity; a property which it never loses; whether under the strongest pressure, or exposed to the greatest artificial cold we are able to produce. In all bodies in which it lodges, or is kept in closestopped vessels for a great number of years, it still remains in a state of permanent fluidity. The next obvious property of the air is, its weight or gravity-a property which was discovered by the immortal Galileo, a celebrated astronomer and mathematician, born in the year 1564. Although Galileo was well acquainted with the weight or gravity of air as a body, yet it is to his ingenious pupil, Torricelli, that wo are indebted for the discovery, that it is the weight and pressure of the atmosphere which keeps water raised in pumps, and mercury raised in barometrical tubes, and that a column of air, of the whole height of our atmosphere, is equal to a column of water of equal base, 34 or 35 feet high, and a column of mercury of an equal base, 30 inches high; hence water never ascends in common pumps higher than 35 feet, or mercury in barometrical tubes higher than 31 inches. If the student (for the use of whom these essays have been principally written) is in possession of an airpump, he will derive considerable advantage from the performance of the following experiment. Take a common glass cylinder, or receiver, open at both ends, and place it upon the plate of the air pump. The experimentalist is now to cover the uppermost open end of the cylinder with the palm of his hand, and exhaust the cylinder of its air. The pressure being now entirely taken off from under the hand, he will immediately become sensible of an almost insupportable weight, which presses down the hand to the receiver, with a force sufficient to cause considerable pain, and indeed to break the hand, if it is not soon removed from its uneasy situation, which can only be done by the re-admission of air into the receiver. Air can be even weighed with as much accuracy as any other substance. The difference of weight between a vessel filled with air, and another vessel exhausted of its air, may be readily ascertained, and this difference will be proportionally more sensible, if the vessel be filled with condensed air. A quart measure of atmospheric air taken near the surface of the earth, weighs about 17 grains. The specific gravity of atmospheric air, as determined by Sir George Shuckburgh, is 0.0012, the barometer being at 30 inches, and the thermometer between 50 and 60 deg. It is, therefore, 816 times lighter than water. I have said that the whole pressure of the atmosphere is equal to a column of mercury of an equal base, and 30 inches high, and as a column of mer cury of this height, and an inch square, is found to weigh 15 pounds, it follows that the pressure of the atmosphere amounts to 15 pounds on every square inch of the earth's surface; consequently, the pressure on every square foot of surface, amounts to 2160 pounds. If we reckon the external surface of a man's body to be about 15 square feet, and the ordinary weight of the atmosphere 2160 pounds on every square foot, he will sustain a weight amounting to nearly 14 tons. The weight of the atmosphere, however, is not always the same, and indeed the difference in its weight from the natural changes in the state of the air is often very considerable, and it would be no difficult task to shew that the difference in the weight of the atmosphere on the surface of a man's body, supposing it, as before, to be equal to 15 square feet, is nearly 1 ton. We have, therefore, no reason to wonder that invalids do so powerfully experience the variation of the additional pressure of the atmosphere; but we have reason to wonder that so great an additional pressure should be borne at all without crushing the frame of our bodies to pieces. But the fact is simply this, the interior cavities of our bodies always contain some elastic fluids, the re-action of which is sufficient to balance the weight of the external atmosphere. an Dr. Vince has given the pressure or weight of this ambient fluid on the whole surface of the earth Dr. at 77,670,297,973,563,429 tons. Cotes reckons the weight equivalent to a globe of lead 60 miles in diameter. And Dr. Thompson gives 11,911,163,227,258,181,818 pounds, avoirdupois, for the whole weight of the atmosphere. As air is elastic fluid, and its density being always proportional to the weight by which it is compressed, it follows that its density diminishes according to its distance from the surface of the earth; consequently, the air on the top of very high buildings is considerably rarer than that at the surface of the earth, whichis compressed by the whole weight of the incumbent atmosphere. Philosophers have demonstrated, that if the altitudes in the air do continually increase in arithmetical proportion, the rarity of the air will be in continued geometrical propor 140 274877906944 1099511627776 For some of the most accurate ex periments relative to the aqueous vapour contained in the atmosphere, I refer the reader to the writings of that excellent chemist, Mr. Dalton, of Manchester. I am well aware of the "A great truth of the ancient maxim, book is a great evil," and I have endeavoured to improve upon this maxim, of the importance of which as a modern writer, I am so well satisfied; but I have already extended this paper to a greater length than I had I am obliged to suppress the latter originally intended, for which reason part of it, containing observations on the existence of those bodies, which, although they cannot be considered as constituent parts of the atmosphere, have been occasionally found in it. I shall therefore conclude with noticing the following principal errors of the press, in my preceding essays, which the candid and liberal reader will please to correct with a pen, the one marked with an asterisk materially affects the sense. Col. 26, line 45, for atmospheric air, read water. Col. 28, line 43, for oxymuriate, read oxymuriatic. Col. 227, line 52, for sulphurat, read sulphuret. Col. 228, lines 45 and 47, for Kerwan, read Kirwan. Col. 228, line 49, for of, read by. Col. read are. Col. 347, line 39, for were, 347, line 55, for was, read is. JOHN NUTTALL. Handsworth Woodhouse, near Sheffield, 15th April, 1822. |