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has rendered to the cause of Christianity ; although perhaps cultivated extensively with a view to very different results. Of how much more value then may we suppose such an agency capable of becoming in the hands of men devoted to the interests of truth, and as earnestly intent on achieving that sublime of human lore-
“To vindicate the ways of God to man!" But, irrespective of these particular adaptations of scientific truths to the purposes of religion, the general effects of Science on the minds and manners of men are such as to render its extensive diffusion a most important and powerful auxiliary to the direct inculcation of Christian doctrine and duty. Foremost among these beneficial influences, must be ranked its pacific tendency. Science and Christianity are indeed equally bound up in the cause of peace-which they severally serve to promote and nourish, as by it they are protected and fostered in return. To the calm and contemplative pursuits of the one, or the mild and gracious precepts of the other, what can we conceive more hostile and destructive than contentiousness and . war? The Roman poet doubtless spoke the result both of his own ex. perience and observation, when he said, that
“Ingenuas didicisse fideliter artes
Emollit mores ; nec sinit esse feros." And if this were true of the scanty measure of Science possessed in his day, with what increased force does the observation apply to the present advanced state of every department of human knowledge? But an enlightened acquaintance with modern Science is capable of effecting much more than the mere refinement of manners. Civilized habits are indeed valuable for their own sake, but chiefly as indications of an educated mind; and this again is invariably accompanied by a corresponding improvement in the moral feelings, tastes, and dispositions. No man's mind can be made the receptacle of lofty and ennobling truths, without his heart becoming at the same time the depository of more pure and generous emotions. It is impossible for any one to become familiar with the many beautiful and instructive discoveries of Science, without having his conceptions of the power and wisdom of the Deity enlarged and refined; or without being led to perceive on every hand new and striking evidences of his benevolence in adapting the constitutions of his creatures to the circumstances in which they are to live, and in providing for their various necessities and wants, as well as of his perfect justice and fairness in administering the government of the universe at large. Nor can any one contemplate the various applications of these discoveries to purposes of usefulness and economy, or of sanitary protection, without being inclined to take brighter and more kindly views of life without feeling himself a happier, as well as wiser, man— without becoming conscious of a new source of sympathy with all ranks and classes of humanity. Look, for instance, at that unpretending, yet truly noble instrument—the miner's safety-lamp, carrying light and life, and industry, into the very bowels of the earth, and setting the most rebellious spirits of nature at defiance. Look at steam-generating itselfannihilating time and space—bringing seas and continents together-grinding rocks to powder, and even converting, with electric speed, water itself into fire-every way working wonders-and, Christianity alone excepted, operating as the most powerful means for the promotion of social progress and civilization that the world has ever witnessed. Next look at the
press-that Dust Doble of human inventions-giving permanence to the evanescence of fancy, and body to the spirituality of thought
* to airs pothing,
A local habitation, and a mne: preserving the wisdom and experience of past ages as our own, and waiting to transmit our present conceptions and characteristics to future times, informing the ignorant, gratifying the learned, and benefitting all. contemplate these triumphs of mind over refractory matter; investigate their origin, and the causes which have combined to their production ; study their history, and examine the principles on which they rest; then look at the recent, and still increasing, accessions to that class of phenomena, which Seience demonstrates to be guided by the operation of certain fixed and ascertainable laws; consider further the admirable simplicity, the uniformity and universality of these natural requirements; their wonderful adaptation to the purposes of human economy and happiness, and their perfect harmony with the divine institutions of providence and grace; and then say whether we have not here evidences of an agency of incalculable power, of inestimable value, and an importance that can scarcely be overrated placed by God himself in human hands, as if for the express purpose of awakening mankind to a sense of their true position, in relation both to the world and himself, and at the same time of furnishing them with a principal means of attaining it. We have seen some of the wonders which Science has already accomplished, so that its power is unquestioned ; we have seen the great and growing influence it bids fair to exercise over the conduct and opinions of men ; its importance, therefore, cannot be denied: we have seen too that its tendencies are of the most beneficial kind, and not less conducive to the physical improvement, than the moral regeneration of mankind; hence its value is determined.
These then are the grounds on which we would rest the claims of Science, to be considered the grand coadjutor of Christianity; and on which we would commend it to all who are concerned in spreading the pure and holy doctrines of the latter, as the most natural and efficient means they can possibly use to awaken and interest the irreligious mind, and thus bring it within the sphere of Christian operations, and, by suitable preparatory culture, render it more disposed to the reception of sublimer, though congenial, truths. But while we look upon this as the natural course, far be it from us to assert the erroneous doctrine that Religion should stand idly by till Science has performed her part in the work of reformation : it is only by co-operating as fellow-labourers, that either can secure complete success. The tree of knowledge may indeed strike its roots deep into the fastnesses of earth, but it is by the sunbeams and dew of heaven that its fruit must be matured and ripened ; and although the seed of the word be sown in the hearts of the children of men,-unless the hand of the husbandman has been also diligent in preparing the soil for its reception, the bounteous showers of heaven will haply descend upon the thorns and brambles, instead of the tender plant, which they choke in its fruitless efforts to reach the light and liberty of day. But when the votaries of Science shall aim at rendering their discoveries the means of advancing and illustrating divine truth, and the recognised teachers of sacred things shall likewise enforcé the precepts of & sound philosophy with the sanctions of religion, then may we hope that "man will assume his station as a rational being, and Christianity achieve her triumpb."
PAPERS ON NATURAL PHILOSOPHY.
CENTRE OF GRAVITY.
We stated, in a former number, that the attraction of gravitation was to be estimated from the earth's centre, which is in fact the point about which all the other parts balance each other, or “the centre of gravity.” This definition equally applies to other bodies. In the case of dense masses, we may support or suspend them by a single point, which we consider to bear all the burden, and therefore term the centre of weight or gravity; and, in the case of liquids, the like might be effected but for their less cohesive attraction. If the centre of gravity be beyond the base of the body-which is ascertained by drawing a perpendicular line from it-its upright position cannot be maintained, and its security may be estimated by the nearness of the perpendicular line to the centre of the base. It is matter of no small moment in many instances rightly to estimate the true position of the centre of gravity, particularly in the case of heavily-laden wagons, which have to traverse rough roads; we frequently observe them, and also stagecoaches, piled to such a height as to endanger the safety of all the travellers. Equally so is it with buildings, only the hazard here is somewhat abated owing to the cohesion subsisting between their several parts, and which will frequently prevent the building from falling, even though the line of direction (as this perpendicular is termed,) be beyond the base. The leaning tower of Pisa is a curious example; and, as an illustration of the nicely-balanced position of the centre of gravity, we cannot give a better than the celebrated Stonehenge.
THE MECHANICAL POWERS. The powers termed mechanical, are simply contrivances for applying force in the most advantageous manner. In number they are six; and all the movements of nature, whether in reference to anatomy, astronomy, or any other branch of physics, as well as in machinery, produced by art, however complex or intricate, each movement can be reduced to the influence of the lever, the wheel and axle, the pulley, the inclined plane, the wedge, and the screw, and even some of these are but compounded of others. There is a grand axiom to be considered in the application of these powers, viz., “ That what is gained in power is lost in time,” which however, it must be confessed, is rather an ambiguous definition. We know that the velocity of a body is the rate of its motion over a certain space; and, therefore, we think that this axiom would be more clearly expressed by saying, “That advantage is gained in proportion as the velocity of the power exceeds the velocity of the weight,” and vice versa. A few illustrations, as we proceed, will exhibit the truth of this definition.
The first mechanical power then is the lever, of which there are three descriptions. 1st. There is the lever which has the fulcrum between the weight and the power.
Suppose A B to represent a lever, the point c being its centre of motion ; on the fulcrum of which, if the lever turn, B comes into the position D, and at the same time A to E. We perceive, in this case, no advantage is gained, because A C, and c B, being equal, they both
travel with the same velocity, or move over an equal space in an equal time. This kind of lever is, however, brought into great practical use in the generality of scales now employed.
Again, in another description of the first kind of lever, we see that the fulcrum is placed much nearer the weight to be raised, than the power (say one-third); consequently, the arm of the lever, E B, being twice as long as E a, it will describe a greater circle in the same time, as E d; or, in other words, travel with greater velocity: and, if our supposition relative to its length be correct, we shall arrive at the conclusion that one pound applied to B, will raise two pounds attached to c.
In the second kind of lever, the power is applied to one end, the other resting on the fulcrum, with the weight between. From an example, we shall see the principle acting as in the former cases. If we compare this diagram with the last, it will be obvious that in each case the weight Wa describes a segment of an equal circumference; and the same rule in that will apply to this,
a c viz., that a pound placed at a, will raise two at D.
In respect to the third description of lever, it will be perceived that the weight is at one end, the fulcrum at the other, and the power in the centre. Taking it on a supposition that the length of the part of the bar, B d, is four times greater than de, we shall find that B, with the weight attached, will travel with four times the velocity of d, the power. We must, therefore, conclude, in accordance with our golden rule, that four pounds power would, in this case, be required to move one pound weight, which is really the fact; for this kind of lever is most disadvantageous, and appears seldom used, except in hoisting ladders, when we see men unable to effect their purpose by the muscles of the arm alone, and therefore call in the aid of their legs, and, standing on the bars, by this means raise the ladder.
The wheel and axle, the next in order to the lever, is manifestly based on the same principle; but whereas a straight bar can only be moved a few inches at a C CIC time, a wheel, through the means of a rope or handle, can continually be turned round, and thus act the part of a perpetual lever, although, of course, for certain offhand purposes, it is not so convenient as the simple bar.
It will be necessary, in order to see its analogy to the lever, to exhibit it endways, thus :
It will now be immediately perceived that the radius, ab, is simply a lever, having the power at one end, the weight at the other, and the fulcrum c, (the common centre to both wheel and axle,) between.
The pulley is the next simple mechanical power; and one of its greatest advantages is, to enable power to be applied through the agency of man, when he himself
could not conveniently exert that power. Thus we find a weight is hoisted to the topmast of a vessel by an individual on deck, which could not be done but by the aid of the pulley.
In reference to the single fixed pulley, as in the lever, no advantage is gained, because the power and the weight travel with equal velocity, or pass over the same space in the same time—just in proportion as the weight ascends the power descends; and this is so, because the wheel acts as a lever with equal arms, so that the weight and power must necessarily S A balance.
In the compound moveable pulley we shall find, as previously, that the power required will be less in proportion as the velocity of the power, is greater than the velocity of I the weight. By referring to the diagram, we see that while the power a requires that all the rope to c should be hoisted, B is only elevated once.
So many moveable pulleys are requisite only on account of distributing the weight over a large surface, or the length of the rope from the fulcrum. If we examine the figure of the lever of the first kind, we find the weight distributed over the whole bar, because it is inflexible ; it is thus that so many moveable pulleys are required, and, of course, by adding fresh blocks, the weight is still more distributed, and less power becomes necessary to move it, although the space to be travelled by the power is thus extended.
ANASTATIC PRINTING.—We have been favoured with an opportunity of inspecting, at the offices of Mr. Joseph Woods, No. 3, Bargeyard Chambers, Bucklersbury, a process of reprinting to which this name has been given. We are aware that many attempts have, at different times, been made to arrive by similar means at an available result. These have been attended by various success, but in no case amounting hitherto to anything profitable. To describe the present result, in as few words as possible,-it is the reproduction of any form of letter-press, or any quality of print, drawing, engraving, or lithograph, in unlimited quantity, in an inconceivably brief space of time. Any journal for instance, say the Times, might in twenty minutes be prepared for reprinting merely from a single number, and worked off with the ordinary rapidity of the steam-press. It is our purpose fully to describe, in the next number of the ART-UNION, the process whereby this is effected, and to show the admirable applicability of the invention to all those kinds of croquis drawings, sketches, &c. &c., which have hitherto been presented to the public eye as wood-engravings, by giving, as a specimen, a page of drawings, by distinguished artists, printed in this manner. The proprietors are scarcely yet prepared to work their patent on the extensive scale which they contemplate. We have, however, seen a set of drawings, fresh from the hands of the artists, prepared for printing, and printed off in little more than a quarter of an hour! In less than a quarter of ar hour from the time of receiving the sketch, the printer will present to the artist proofs of his work, which shall resemble the original as perfectly as if it had been reflected on the paper touch for touch. In presenting these specimens, we shall describe the process at length in the next number of the ART-Union. In the meantime it must be observed, that it is impossible to define the development of this, to say the least, truly wonderful invention, whereby the work of the artist is reproduced in fac-simile without the slightest point of difference, the finest and rarest engravings may be reprinted ad infinitum,-and, last, thongh not least, books may be reprinted, as from stereotypes, in unlimited quantity.Art-Union,