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Were the working miners carefully instructed ir the nature and composition of the atmosphere, and its chymical properties, and particularly in the nature and composition of the difserent gases,<-were such instructions illustrated by a judicious selection of chymical experiments, and were the proper practical hints and precautions deduced and clearly exhibited, there cannot be the least doubt that it would be attended with numerous beneficial results. When a person is ignorant of the noxious principles that may be secretly operating within the sphere of his labours, he will frequently rush heedlessly within the limits of danger; whereas, a man who is thoroughly acquainted with all the variety of causes which may possibly be in action around him, will proceed in every step with judgment and caution, and, where danger is apparent, will hasten his retreat to a place of safety. The injuries which are produced by the stroke of lightning form another class of accidents which are frequently owing to ignorance. It is still to be regretted, that, notwithstanding the discoveries of modern philosophy, respecting the 2lectric fluid and the laws of its operation, no hunderguard has yet been invented, which, in all situations, whether in the house, in the street, in the open field, in a carriage, or on horseback, shall serve as a complete protection from the ravages of lightning. Till some contrivance of this kind be effected, it is probable that the human race will still be occasionally subjected to accidents from electrical storms. Such accidents are more numerous and fatal, even in our temperate climate, than is generally

with it, and even work by its light in the midst of those explosive mixtures which have so often proved fatal when entered with a common lamp or a candle. It transmits its light, and is fed with air, through a cylinder of copper wire-gauze. The aper. fures in the gauze are about one-twentieth or onetwenty-fifth of an inch square, and the thickness On the wire from one-fortieth to one-sixtieth of an inch diameter. The parts of the lamp are:–1. The brass cistern which contains the oil. 2. The rim in which the wire-gauze cover is fixed, and which is fastened to the cistern by a moveable screw. 3. An aperture for supplying oil, fitted with a screw or cork, and a central aperture for the wick, 4. The wire-gauze cylinder, which consists of at least 625 apertures to the square inch. 5. The second top, three-fourths of an inch above the first, surmounted by a brass or copper plate, to which the ring of suspension is fixed... 6. Four or six thick vertical wires, joining the cistern below with the top plate, and serving as protecting pillars round the cage. When the wire-gauzé safety lamp is lighted and introduced into an atmosphere gradually mixed with fire-damp, the first effect of the fire-damp is to increase the length and size of the flame. When the inflammable gas forms one-twelfth of the volume of the air, the cylinder becomes filled with a feeble blue flame, but the flame of the wick appears burning hrightly within the blue sla::c, and the light of the wick increases, till the fire damp increases to one-fifth, when it is lost in the flame of the firedamp, which fills the cylinder with a pretty strong light. As long as any explosive mixture of gas exists in contact with the lamp, so long will it give its

imagined. From an induction of a variety of facts of this kind, as stated in the public papers and other periodical works, in the year 1811, the author ascertained that more than twenty persons were killed by lightning, or at the rate of a thousand persons every fifty years, during the summer months of that year, within the limits of our island; besides the violent shocks experienced by others, which did not immediately prove fatal, and the damage occasioned to

light, and when it is extinguished, which happens when the foul air constitutes one-third of the volume of the atmosphere, the air is no longer proper for respiration, for though animal life will continue where flame is extinguished, yet it is always with suffering.

DAVY's safety LAMP.

The following are the principal parts of the safety lamp:-F is the lamp throwing up a brilliant flame. C is the reservoir, supplied with oil by the tube M. E E is a frame of thick wire to protect the wireuze, A A A A, which has a double top G. H. The me has a ring Pattached to it for the convenience of carrying it. The wire-gauze is well fastened to the rim B. Notwithstanding the utility of this invention, such is the carelessness and apathy of the working miners, that they either neglect to use their safety lamps, or to attend to the means requisite to keep them in order, which carelessness and apathy are the effects of that gross ignorance into which so many of them are sunk. Hence we find, that seldom o . "o: we do not hear of destructive explosions happening in our coal m particularly in England. ng ines,

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shees and cattle, and to public and private edifices; and it is worthy of notice, that most of the individuals who were killed by the lightning had either taken shelter under trees, or were in situations adjacent to bells or bell-wires. The experience of succeeding years proves that a similar number of disasters of this kind annually take place. It is, however, more than probable, that at least half the number of accidents arising from the same cause might have been averted, had the nature of lightning, and the laws which regulate its movements, been generally known. Seldom a year passes but we are informed by the public prints of some person or other having been killed by lightning, when taking shelter under a large tree, of whole families have been struck down when crowding around a fire-place, during a thunder-storm, of one person having been struck when standing beside a bell-wire, and another while standing under a bell connected with the wire, or under a lustre hanging from the ceiling. There can be little doubt, that a considerable number of such accidents would have been prevented, had the following facts respecting the nature of lightning been extensively known:— That lightning is a fluid of the same nature, and is directed in its motions by the same laws which regulate the motions of the electric fluid in our common electrical machines;—that it is attracted and conducted by trees, water, moisture, flame, and all kinds of metallic substances; —that it is most disposed to strike high and pointed objects; and that, therefore, it must be dangerous to remain connected with or in the immediate neighbourhood of such objects when a thunder-cloud is passing near the earth. Hence the following precautionary maxims have been deduced, by attending to which the personal accidents arising from thunder-storms might be in a great measure prevented. In the open air, during a storm, rivers, pools, and every mass of water, even the streamlets arising from a recent shower, should be avoided, because water being an excellent conductor, might determine the course of an electrical discharge towards a person in contact with it, or in its immediate neighbourhood. All high trees and similar elevated conductors should also be avoided, as they are in more danger of being struck than objects on the ground; and, therefore, a person in contact with them exposes himself to imminent danger, should the course of the lightning lie in that direction. But, to take our station at the distance of thirty or forty paces from such objects, or, at such a distance as may prevent us from being injured by the splinters of wood, should the tree be struck, is more secure than even in the midst of an open plain. Persons in a house not provided with thunder-rods, should avoid sitting near a chimmey or fire-place, whether there be a fire in the

grate or not. For when there is a fire in the grate, the fire contains the following conductors, flame, smoke, rarefied air, and soot. Even when there is no fire, the soot with which the flue is lined is a conductor; and from the superior height of the chimney-shaft above every other part of the building, it is more liable than any other part of the house to be struck with lightning. In a house, too, gilt mirrors or picture-frames, lustres or burning candles, bell-wires, and all metallic substances, should be carefully avoided, as they asford so many points of attraction, which might determine the course of an electric discharge. The safest position is in the middle of the room, if not near a lustre, a bell, or any thing hanging from the ceiling; and if we place the chair on which we sit on a bed or mattress, almost every possible danger may be avoided " Such are a few maxims easy to be recollected and put in practice, by attending to which, not a few accidents from electrical explosions might be averted. In the next place, various accidents have happened from ignorance of certain plain mechanicol principles. For example, serious accidents have sometimes occurred from the want of acquaintance with the laws of motion. Persons have heedlessly jumped out of moving vehicles, and got their legs and arms sprained or dislocated, and from one boat to another when both were in rapid motion, and run the risk of being either bruised, drenched, or drowned. But had the effects of compound motion been generally known and attended to, in all those cases where it occurs, it would have prevented many of those accidents which have happened from persons rashly jumping out of carriages when in rapid motion, or attempting to jump from the top of a moving cylinder, in which cases they are always precipitated with violence in a direction disferent from what they expected, from the obvious effects of a combination of forces. Boats and carriages have been sometimes overset by persons rising hastily when they were in danger of such accidents, from ignorance of the principle, that the centre of gravity of the moving vehicle, by such a practice, is raised so as to endanger the line of direction being thrown beyond the base, when the vehicle must, of course, be overturned; whereas, had they clapped down to the bottom, they would have brought down the line of direction, and consequently the centre of gravity, farther within the base, so as to have prevented the accident and secured their safety.

* It has been generally thought that the cellar is the most secure situation during a thunder-storm, but this is true only in certain cases. When the lightning proceeds from the clouds, it is unquestion' ably the most secure position; but in the case of a returning stroke, or when the lightning proceeds from the earth, it is less secure than the higher parts of the building.

The reason of this will perhaps more plainly appear from the following explanations:—The centre of gravity is that point of a body about which all its parts are in equilibrio, or balance each other; and consequently, if this point be supported, the whole body will be at rest, and cannot fall. An imaginary line drawn from the centre of gravity of anybody towards the centre of the earth is called the line of direction. Bodies stand with firmness upon their bases, when this line falls within the base; but if the line of direction falls without the base, the body will be overturned. Thus, the inclining body ABCD, whose centre of gravity is E, stands firmly on its base CDKF, because the line of direction EM falls within the base. But if a weight, as ABGH, be laid upon the top of the body, the centre of gravity of the whole body and weight together is raised up to I; and then as the line of direction ID falls without the base at D, the centre of gravity I is not supported, and the whole body and weight must tumble down to

gethor.

The tower of Pisa, in Italy, leans sixteen feet out of the perpendicular, so that strangers are afraid to pass under it; but as the plummet or line of direction falls within its base or foundation, it is in no danger of falling, if its materials keep together; and hence it has stood in this state

for three hundred years. But were an additional erection, of any considerable elevation, to be placed upon its top, it would undoubtedly soon tumble into ruins. To a somewhat similar cause, in combination with heedlessness and ignorance, may be ascribed many of those accidents which so frequently happen at spinning mills and other pieces of machinery, by which legs and arms are torn asunder, and the human frame sometimes mangled and destroyed. Fatal accidents have likewise happened from ignorance of the effects produced by the refraction of light. It is a well-known optical fact, that when a ray of light passes from air into water, and is again refracted, the sine of the angle of incidence is in proportion to the sine of the angle of refraction as four to three. From this circumstance it happens, that pools and rivers appear shallower than they really are—their channels, when viewed from their brink, being apparently higher than their true position, in the proportion of three to four; so that a river eight feet deep will appear from its bank to be only six. This fact may be at any time perceived in a tub or pail full of water, where the bottom of the vessel will obviously appear to be raised a considerable space above its true position, and its apparent depth consequently diminished. In consequence of this optical illusion, which is not generally known, many a traveller as well as many a schoolboy has lost his life, by supposing the bottom of a clear river to be within his depth, as, when he stands on the bank, the bottom will appear one-fourth nearer the surface than it really is. This will appear evident from the following illustrations :—If a ray of light AC passes obliquely from air into water, instead of continuing its course in the direct line CB, it takes the

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direction CH, and approaches the perpendicular PP, in such a manner, that the angle of refrac

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30, ON THE GENERAL DIFFUSION OF KNOWLEDGE.

tion PCH is less than its angle of incidence ECA. AE is the sine of the angle of incidence, and HP the sine of the angle of refraction; and the proportion they bear to each other is as four to three. If a small body, therefore, were placed at H and viewed from the point A, it would appear as if it were raised to the point B, or one-fourth higher than it really is.

This may be farther illustrated by the following common experiment. Put a shilling into the bottom of an empty bason, at C, and walk backwards till it appear completely hid by the interception of the edge of the bason; then cause water to be poured into the bason, and the shilling will instantly appear as if placed at the point D : for, being now in a denser medium, it appears raised, or nearer to its surface. Before the water was poured in, the shilling could not be seen where it was ; now it is seen where it is not. It is not the eye that has changed its place, but the ray of light has taken a new direction, in passing from the water to the eye, and strikes the eye as if it came from the piece of money. This experiment may be varied as follows:–Take an empty bason, and, along the diameter of its bottom, fix marks at a small distance from each other, then take it into a dark room, and let in a ray of light; and where this falls upon the floor, place the bason, so that its marked diameter may point towards the window, and so that the beam may fall on the mark most distant from the window. This done, fill the bason with water, and the beam which before fell upon the most distant mark, will now, by the refractive power of the water, be turned out of its straight course, and will fall two or three or more marks nearer the centre of the bason.

It is owing to the circumstance now stated, that an oar partly in and partly out of the water appears broken; that objects appear distorted when seen through a crooked pane of glass; that a fish in the water appears much nearer the surface than it actually is; and that a skilful marksman, in shooting at it, must aim considerably below the place which it seems to occupy. It is owing to the refractive power of the atmosphere, that the sun is seen before he rises above the horizon in the morning, and after he sinks beneath it in the evening; that we sometimes

see the moon, on her rising, totally eclipsed, while the sun is still seen in the opposite part of the horizon; and that the stars and planets are never seen in the places where they really are, except when they are in the zenith, or point di. rectly over our head. Many affecting and fatal accidents have happened, and are frequently recurring, particularly to children, and females in the higher ranks of life, from their clothes catching fire, most of which might be prevented, were the two following simple facts universally known and practically applied, that flame has a tendency to mount upwards; and that air is essentially requisite for supporting it. When the clothes of females take fire, as the fire generally begins at the lower parts of their dress, so long as they continue in an upright posture the flames naturally ascend, and meeting with additional fuel as they rise, become more powerful in proportion; whereby the neck, the head, and other vital parts of the body are liable to be most injured; and, by running from one part of the room to another, or from one apartment to another, as is most frequently the case, the air, which is the fuel of fire, gains free access to every part of their apparel, and feeds the increasing flame. In such cases, the sufferer should instantly throw her clothes over her head, and roll or lie upon them, in order to prevent the ascent of the flames and the access of fresh air. When this cannot conveniently be effected, she may still avoid great agony, and save her life, by throwing herself at full length on the floor, and rolling herself thereon. Though this method may not, in every case, completely extinguish the fame, it will to a certainty retard its progress, and prevent fatal injury to the vital parts. When assistance is at hand, the by-standers should immediately wrap a carpet, a hearth-rug, a great coat, or a blanket, around the head and body of the sufferer, who should be laid in a recumbent position, which will prove a certain preventive from danger. During the year 1813, the author noted down more than ten instances, recorded in the public prints, of females who were burned to death by their clothes catching fire, all of which might have been prevented, had the simple expedients now stated been resorted to and promptly applied. It may be remarked, in the next place, that many of the diseases to which mankind are subject—particularly fevers, smal.-pox, and other infectious disorders—might be prevented by the diffusion of knowledge in relation to their nature, their causes, and the means of prevention. It cannot have been overlooked, in the view of the intelligent observer, that fevers and other infectious disorders generally spread with the greatest facility and make the most dreadiul havoc among the lower orders of society. This is owing, in part, to the dirty state in which

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their houses are kept, every part of which as: sords proper materials for the production and detention of pestilential effluvia, and their ignorance of the importance of pure atmospherical air to animal life, and the consequent necessity of daily ventilating their apartments. It is also owing in a great measure to the custom of persons crowding into the chambers of those who are labouring under such infectious diseases, and thereby not only increasing the strength of the infectious virus, but absorbing a portion of it in their own bodies, to spread its baleful influence in a wider circle. Such a conduct frequen ly proceeds from a want of conviction of the infectious nature of such disorders, and from ignorance of the rapid manner in which they are sometimes communicated from one to another, as well as from that obstinacy and from those inveterate prejudices which are always the accompaniments of ignorance. Though the cow-por inoculation has been proved by experience to be an effectual preventive of that loathsome and often fatal disorder, the small-pox, yet numbers in the lower ranks of life cannot yet be persuaded to use this simple preventive, and will rather run the risk of experiencing all its disagreeable and dangerous effects both on their own persons and on those of their offspring. Their obstinate preiudices, in this and similar respects, are increased by their false views and reasonings respecting the doctrine of the divine decrees, and the providence of the Almighty. They imagine, that to induce one species of disease for the prevention of another is attempting to take the government of the world out of the hands of the Creator, and that no means of preventing disorders can be of any avail, if the Deity has otherwise decreed; not considering that the Almighty governs the world he has created by regular and invariable laws, and accomplishes his decrees through the intervention of those secondary causes, both natural and moral, which are continually operating in the physical and intellectual world. Were general knowledge more extensively diffused, and the minds of the multitude habituated to just principles and modes of reasoning, such fallacious views and opinions would be speedily dissipated, and consequently those physical evils and disorders which they produce would be in a great measure prevented. Again, to ignorance we must likewise attribute, in a great measure, the pernicious effects of contaminated air in dwelling-houses. Pure air is essentially requisite to the health and vigour of the animal system as wholesome food and drink. When contaminated by stagnation, by breathing, by fires or candles, it operates as a slow poison, and gradually undermines the human constitution; yet nothing is less attended to in the economy of health by the great majority of mankind. Because air is an invisible

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substance, and makes little impression on th: organs of sense, they seem to act as if it had 1.0, existence. Hence we find, that no attention is paid by the lower orders of society to the proper ventilation of their apartments. In some cases, the windows of their houses are so fixed in the walls as to be incapable of being opened, and in other cases, where the windows are moveable, they are seldom opened, except by accident, for weeks and months together; and were it not that a door and a chimney are to be found in every habitable apartment, the air would be rendered in many instances absolutely unfit for respiration. Crowds of tailors, weavers, shoemakers, and other mechanics, employed in sedentary occupations, are frequently pent up in close, and sometimes damp apartments, from ning till evening, without ever thinking of opening their windows for a single half hour for the admission of fresh air; and consequently, are continually breathing an atmosphere highly impregnated with the noxious gas emitted from the lungs, and the effluvia perspired from their bodies, which is most sensibly felt by its hot suffocating smell, when a person from the open air enters into such apartments. The sallow complexion of such persons plainly indicates the enervating effects produced by the air they breathe; and although its pernicious effects may not be sensibly felt, it gradually preys upon their constitutions, and of en produces incurable asthmas, fevers, consumptions, and other dangerous disorders, which are frequently imputed to other causes. Nothing is more casy than to open the windows of an apartment, and other apertures that communicate with the external air, at meal hours, when the room is empty, in order to expel the contaminated air, and admit the pure vital fluid. No me licine or restorative is cheaper or of more importance to health and vigour than pure atmospherical air; yet, because it costs nothing, it is little regarded. Hints and admonitions in reference to this point are seldom attended to; for ignorance is always proud and obstimate, and the inconveniences supposed, in certain cases, to flow from the practice of ventilating particular apartments are seldom attempted to be remedied. It is, therefore, presumed, that were a knowledge of the nature of the atmosphere, of the ingredients that enter into its composition, of its indispensable necessity for the support and invigoration of animal life, of the circumstances by which it is deteriorated, and of the baneful effects which are produced by its contamination, more widely diffused, its use and importance would be more duov appreciated, and the disorders which flow from the circumstances now stated effectually prevented.*

* The following fact shows, in an impressive man. ner, the danger arising from the want of a free circulation and frequent change of air. “In the lying

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