The digester is another instrument of very great power, and sufficiently discovers the amazing force of air, when its elasticity is augmented by fire. A common tea-kettle, if it was strong enough with the spout closed up, and the lid put firmly down, would serve as a digester. But the proper instrument used for this purpose is a strong metal pot, with a lid to screw close on, so that, when down, no air can get in or go out into this pot meat and bones are put, with a small quantity of water, and then the lid is screwed close, a lighted lamp is put underneath, and, what is very extraordinary, yet equally true, in eight or ten minutes, the whole mass, bones and all, are dissolved into a jelly-so great is the force and elasticity of the air contained within, struggling to escape, and breaking in pieces all the substances with which it is mixed. Care, however, must be taken not to heat this instrument too violently, for then the inclosed air would become irresistible, and burst the vessel with an explosion which might, perhaps, be fatal. On the same principle as the foregoing does that culinary utensil act which is also called a digester: only this latter has a small vent in the lid, which, when the vessel is fully heated, the force of the air within lifts up, whereby the steam escapes: the power of this instrument is consequently much less than the other, but sufficient, however, to extract all the marrow, and every nutritive juice from all the bones which are stewed in it. Such is the economical utility of this vessel, especially in these times of scarcity, that every prudent family, which knows its service, will not be without one. There are many other useful instruments made, which depend on the weight, the elasticity, or the fluidity of the air, which do not come within the compass of our work-as our design is not to give an account of the inventions which curious men have made to determine the nature and properties of air, but a mere narrative of its effects. The description of the pump, the forcing pump, the fire engine, the steam engine, the syphon, and an hundred others, belong not to the naturalist, but to the experimental philosopher: the one gives an history of nature as he finds she presents herself to him, and he draws the obvious picture: the other pursues her with close investigation, tortures her by experiments to give up her secrets, and measures her latent qualities with laborious precision. Much more might, therefore, be said of the mechanical effects of air, and of the conjectures that have been made concerning the form of its parts; how some have supposed them to resemble little hoops coiled up in a spring; others like fleeces of wool; others that the parts are endued with a repulsive quality, by which, when squeezed together, they endeavour to fly off and recede from each other. We have already noticed the disputes relative to the height to which this body of air extends above us, concerning which we see there is no agreement. The disputes and conjectures of philosophers would furnish us with many other ideas upon the same theme, as, How much of the air we breathe is elementary, and not reducible to any other substance? and, Of what density would it become if continued down to the centre of the earth? Then, by the help of figures and a bold imagination, we might shew, that, at the centre, it would be twenty thousand times heavier than its bulk in gold. By the same method we might also prove, that, when raised to the surface of the atmosphere, it is millions of times purer than upon earth. But such speculations do not belong to natural history, and they have hitherto been but of little service to experimental philosophy. It may be of more service to remark something on the different degrees of salubrity in the atmosphere. The air on the tops of hills is generally more salubrious than that in vallies. Dense air is more proper for respiration than such as is more rare, especially for persons afflicted with phthisic or asthma; yet the air on mountains, though much more rare, is more free from phlogistic vapours than that of vallies and lower grounds. Hence it has been found, that people can live very well on the tops of mountains, where the barometer sinks to fifteen or sixteen inches. M. de Saussure, in his journey on the Alps, having observed the air at the foot, at the middle, and on the summits of various mountains, observes, that the air of the very low plains seems to be less salubrious; that the air of the very high mountains is neither very pure, nor, upon the whole, seems so fit for the lives of men, as that of a certain height above the level of the sea, which he estimates to be about two or three hundred toises, that is about four hundred and thirty or six hundred and fifty yards. The air of a bed room has been examined at night, and in the morning after sleeping in it, and it has been generally found, that after sleeping in it, the air has been less pure than at any other timeHence appears the injury to health from very close chambers, curtains, and shutters. The air of privies, even in calm weather, has not been found to be so much dephlogisticated as might have been expected from its disagreeable smell. From this, and other observations, it has been concluded that the exhalations from human excrements are very little injurious, except when they become putrid, or proceed from a diseased body; in which case they greatly infect the air, and very quickly too. Dr. Ingenhousz found by experiment that air at sea, and, in general, air along the shore, is purer, and fitter for animal life, than air on land. Hence, perhaps, the practice of modern physicians in sending consumptive persons to the coasts, or prescribing to them a voyage. On the whole, notwithstanding the experiments of philosophers, and all their conjectures, Providence has given us air generally fit for respiration, and all the common purposes of life, every where, and at every season, and has allowed us a certain latitude, or power of living and being in health in qualities of air which differ to a considerable degree. We do not mean to deny the existence of certain kinds of noxious airs in some particular places, but only say, in general, that the air is good every where, and that the small existing differences are not o be feared so much as some people would make us believe. But it will be necessary for us to take a further view of the air; and we shall find by inspection, that the fluid in which we breathe is fat from being a pure elementary substance. Air, such as we find it, is one of the most compounded bodies in all the compass of nature.Philosophers have considered our atmosphere as one large chemical vessel, in which an infinite number of various operations are constantly performing. In it all the bodies of the earth are continually sending up a part of their substance by evaporation, to mix in this great alembic, and to float awhile in common. Here minerals, from the lowest depths, ascend in noxious or in warm vapours, to make a part of the general mass: seas, rivers, and subterraneous springs, furnish their copious supplies; plants receive and return their share, and animals, that, by living upon, consume this general store, are found to give it back in greater quantities when they die. Water 'may be reduced to a fluid every way resembling air, by heat, which, by cold, becomes water again. Every thing we see gives off its parts to the air, and has a little atmosphere of its own floating around it. The rose is encompassed with a sphere of its own odorous particles, while the hemlock and the night-shade infect the air with scents of a more ungrateful nature. The perfume of musk flies off in such abundance, that the quantity remaining becomes sensibly lighter by the loss. A thousand substances that escape our senses we know to be there: the powerful emanations of the loadstone, the effluvia of electricity, the rays of light, and the insinuations of fire. Such are the various substances through which we move, in which we breathe, and which we are constantly taking in at every pore, and returning again with imperceptible discharge. This great solution, or mixture of earthly bodies, is continually operating upon itself, which, some have thought, is the cause of its unceasing motion; but it operates more visibly upon such gross substances as are exposed to its influence, for scarce any substance is found capable of resisting the corroding qualities of the air. The air, say the chemists, is a chaos, furnished with all kinds of salts and menstruums, and therefore it is capable of dissolving all kinds of bodies. It is well known that copper and iron are quickly covered and eaten with rust; and that in the climates near the equator, no art can keep them clean. In those countries the instruments, knives, and keys that are kept in the pocket, are nevertheless quickly incrusted; and the great guns, with every precaution, after a few years, become useless by excessive rust. Stones, as being less hard, may be readily supposed to be more easily soluble. The marble of which the noble monuments of Italian antiquity are composed, altho' in one of the finest climates in the world, nevertheless shew the impressions which have been made upon them by the air. In many places they seem worm-eaten, and, in others, they appear crumbling into dust. Gold alone seems to be exempted from this general state of dissolution it is never found to contract rust, though exposed to the air ever so long: the reason of this seems to be that sea salt, which is the only menstruum capable of acting upon and dissolving gold, is but very little mixed with the air; for salt being a very fixed body, and not apt to volatilize and rise with heat, there is but a small proportion of it in the atmosphere. In the elaboratories and shops, however, where salt is much used, and the air impregnated with it, gold is found to rust as well as other metals. Bodies of a softer nature are obviously destroyed by the air. Mr. Boyle says, that silks brought to Jamaica, will, if there exposed to the air, rot even while they preserve their colour; but if kept therefrom, they retain both their strength and gloss. The same happens in Brazil, where their clothes, which are black, soon turn of an iron colour, though, in the shops, they preserve their proper hue. In these tropical climates also, such are the putrescent qualities of the air, that white sugar will sometimes be full of maggots. Drugs and plasters lose their virtue, and become verminous. In some places they are obliged to expose their sweetmeats by day to the sun, otherwise the night-air would quickly cause them to putrify. On the contrary, in the cold arctic regions, animal substances, during their winter, are never known to putrify; and meat may be kept many months without any salt whatever. This experiment happily succeeded with eight Englishmen who were accidently left upon the inhospitable coasts of Greenland, at a place were seven Dutchmen had perished but a few years before; for killing some rein-deer for their subsistence, and having no salt to preserve the flesh, to their great surprize, they soon found that it did not want any, as it remained sweet during their eight months continuance upon that shore. These powers, with which air is endued over unorganized substances, are exerted in a still stronger manner over plants, animals of an inferior nature, and lastly, over man himself. Most of the beauty and luxuriance of vegetation, is well known to be derived from the benign influence of the air and every plant seems to have its favourite climate, not less than its proper soil. The lower ranks of animals also, seem formed for their respective climates, in which only they can live. Man alone seems the child of every climate, and capable of existing in all. However, this peculiar privilege does not exempt him from the influences of the air; he is as much subject to its malignity, as the meanest insect or vegetable. With regard to plants, air is so absolutely necessary for their life and preservation, that they will not vegetate in an exhausted receiver. All plants have within them a quantity of air, which supports and agitates their juices. They are continually imbibing fresh nutriment from the air, to increase this store, and to supply the wants which they sustain from evaporation. When therefore, the external air is drawn from them, they are no longer able to subsist. Even that quantity of air which they before were possessed of, escapes through their pores into the exhausted receiver; and as this continues to be pumped away, they become languid, grow flaccid, and die. However, the plant or flower, thus ceasing to vegetate, is kept, by being secured from the external air, a much longer time sweet, than it would have continued, had it been openly exposed. TO BE CONTINUED. YOUR correspondent Inquiro asks, "Is the doctrine of a divine satisfaction given by Christ to the Father, a Scriptural doctrine, or are we to class it among the inventions of men?" I will say something in reply to this question; and should any of your readers suppose my thoughts on the subject to be erroneous, shall be glad to be led by them to better views thereof. We are no where told, in the Scriptures, that Christ gave to his Father a divine satisfaction for sinners; nor is the word satisfaction ever applied, by the writers of the New Testament, to the sufferings and death of Christ: if then the doctrine be scriptural, it must either arise from facts stated in the scriptures, or be necessarily implied in other forms of expression used by the sacred writers; for if the doctrine of satisfaction be not a necessary consequence of any fact recorded in Scripture, and be not necessarily implied in any form of expression used there, I know not what authority we have to call it a scriptural doctrine. I am aware that things have been stated as scriptural facts which, if really so, would render a divine satisfaction to the Father absolutely necessary, in order to the salvation of sinners; but it is denied that such things are scriptural, and contended that facts clearly stated in the Scriptures prove the doctrine of satisfaction to be erroneous. The idea of Christ's giving the Father a satisfaction for sinners, proceeds on the supposition of some change having been produced in the disposition of God towards his creatures, through the intervention of sin; though this, perhaps, the advocates for this doctrine will not admit, however strongly implied in their representation of the subject. Is it not common for them to represent God as a being inflated with wrath-agitated by furious passions-the subject of revengeful feelings and every vindictive principle? and that nothing short of pouring out all his wrath, venting all his fury, and glutting his utmost vengeance upon some one, either innocent or guilty, could possibly pacify, or give him satisfaction? Could such a description of the Father of mercies be admitted as just and scriptural, the doctrine of satisfaction would follow as a natural consequence, and we might say with the Poet, "Rich were the drops of Jesu's blood That calm'd his frowning face; |