earthly light grow pale and fade; and, as he fixes his steadfast gaze, the face of the beholder shines, and he is transformed into a nearer resemblance to Jesus, the friend whom his soul loveth. With such a friend at hand, and heaven in prospect, the fading rays of evening are full of beauty; for they point to the coming dawn of a "morning without clouds." The gradual change from the laden bough and the yellow harvest, to the leafless "tree, and stripped and barren earth, are perceived, not with sadness, but with cheerful hope; for years are ever passing, and ever bringing nearer the great and final change; and, when the seed, sown by the heavenly Husbandman, shall, under the constant influences of his sun and showers, have yielded fruit to his glory, He will gather it into his garner. All the chaff that mingles with it now, shall be separated, for nothing that defileth can be admitted there. But not one grain of wheat, however small, shall be despised or lost; for each is precious in the sight of Him who sowed and ripened it.

M. L. D.

TWELFTH WEEK-MONDAY.

PROSPECTIVE

POWER.

IMPROVEMENT OF LOCOMOTIVE ROTARY STEAM-ENGINE-ELECTRO-MAGNETIC ENGINE.

THE practice of locomotion, by means of steam, is yet in its infancy; and in this age of invention, we need not be surprised to find men of ingenuity actively employed in attempts to discover new and more useful modes of applying this wonderful power to an object of so much importance. The chief defect of the steamengine, in its present form, as applicable to locomotion, consists in the necessary weight and bulk both of the machinery itself, and the coals and water required for the boilers. This is a disadvantage which, though not felt in stationary engines, forms so great an impediment to the locomotive principle, that any scheme by which it could be obviated or diminished, while other proper

ties should remain the same, could not fail to be regarded as highly important.

The weight of the requisite machinery is chiefly owing to the complicated apparatus connected with the movement of the pistons. A plan for dispensing with the pistons altogether, and thus greatly simplifying the mechanism, has lately been adopted, with apparent success, in America, by recurring to the method by which the power of steam was originally, and at a very early period, employed in the direct production of rotary motion. Should this power be found, when tried on a large scale, to answer the sanguine expectations of its advocates, a most desirable saving would be effected in the weight and complicated nature of the mechanism.*

*I allude to Avery's rotary steam-engine, which was first rendered available for moving machinery in America, and has recently been introduced into Great Britain, by Mr. Craig of Edinburgh, by whom patents have been obtained. This engine is formed on the principle discovered by Hero of Alexandria, so far back as the second century before the Christian era; but it has never, till now, been considered of sufficient power to be employed for any useful purpose. In this engine, the steam is conveyed from the boiler by a pipe, to a hollow axle, on which are fixed two oblate hollow arms, enclosed in an iron case. Through this case, the axle passes and revolves in collars or bushes of hemp, which prevent the escape of steam. On the same axle, and outside the case, is a pulley, over which is placed a belt, to communicate the power for any purpose required. The steam, on passing from the boiler, enters the hollow axle, and, by openings from it, into the two arms; at the extremity of each arm, and on opposite edges, is an aperture, through which the steam escapes into the iron case, from whence it is taken off by a pipe. The uniform pressure of the steam at the end of the arms being destroyed by the two apertures, the arms are made to revolve with a force proportioned to the area of the apertures, and the pressure of the steam in the boiler. The axle being made of cast steel, highly polished, and revolving in bushes or collars of hemp, (which are always kept moist by the steam,) there is almost no friction; and thus the whole power is given out, as described, at the end of the arms, which, being fixed on the axle, impel it with a constant, uniform, steady motion. The constructing of one of these engines, of fifteen horse power, was successfully completed by Mr. Ruthven of Edinburgh, on the 12th of September, 1837 ;-it has since been constantly in use in his works, and has given the greatest satisfaction. It has now (April, 1838) been upwards of seven months constantly employed, and, I am informed, without having cost, during that time, one penny a week for oil or tallow, and not a farthing for any repair; while, from its

This mode of applying steam-power, however, would scarcely affect the quantity of coals and water which must be consumed in generating it; and, indeed, so long as steam is resorted to, as the impelling agent, we can expect no great diminution in the use of these articles. But there are in Nature other agents of tremendous force, to which, could they be made subservient to the will of man, a similar objection would not apply; and it is by no means chimerical to suppose, that human ingenuity has as yet only touched on a territory where elements of power remain to be developed, capable of a far more extensive and useful application, than any hitherto employed.

In making this observation, I particularly allude to the very recent discovery of a method of applying to machinery a power generated through means of magnetism; an agent hitherto regarded more as a subject of curious experiment, than as possessing any mechanical value. Since it already seems possible, that, at no distant date, this invention may be generally adopted in many cases in which steam-power is now used, and especially for the purposes of locomotion, it may not be deemed superfluous to devote the remainder of this paper to so interesting a subject.

An artificial magnet need hardly be described. It consists of a bar of iron or steel, which, having been subjected to a certain wellknown process, acquires the property, when suspended horizontally by a single fibre of untwisted silk, or nicely balanced on a pivot, of arranging itself, after a few oscillations, in a "direction nearly simplicity, an important saving in fuel is obtained. Engines of this construction are rapidly coming into use in this country, and their advantages have, for several years, been well understood in America.

It may be stated as a remarkable application of the power of this engine, that a tilt hammer is now worked by it. This is a large hammer, raised about three feet high by a power derived from the engine, and then allowed to fall on a bar of steel or iron, on which its immense weight produces any effect required. Mr. Ruthven's engine is employed in boring, turning, and planing iron; turning two grindstones; and in pumping water and forcing it into the boiler. In addition to the tilt hammer, a blowing machine for his forges is also preparing to be added to it.

north and south, the ends being in consequence denominated, respectively, the north and south poles of the magnet. If we suspend two such bars near each other, it will be seen that the poles in each, which bear the same name, and which, when the magnets were separate, pointed the same way, repel each other with violence, while the north pole of the one, strongly attracts the south pole of the other, and vice versa.

*

It is not necessary, however, that these bars should always be straight. They They are often bent into the form of a horseshoe or semicircle; and in this shape they retain the properties of attraction and repulsion which have just been noticed. It is by means of such magnets that one of the simplest examples of the mechanical application of the principle I have mentioned, has been exhibited; and in the following manner :-Fix two semicircular magnets horizontally in the same plane, so that the north and south poles of the one shall be opposite to the south and north poles of the other respectively, and at the distance of about an inch. Suspend in the interval between them a bar magnet of sufficient size, and observe the position it will take. It will immediately be attracted by the fixed magnet, whose north and south poles are nearest to its own south and north poles, and will cling to it with a force proportioned to the power of the magnet. Next reverse the position of the semicircular magnets, by turning them simultaneously, so that their north poles shall change places with their south poles; the bar will of course undergo a corresponding change. By the aid of a substantial wooden pendulum, into which the bar is fixed, and which is nicely hung on knife edges, a reversing apparatus may be worked, and when the machine is once set agoing, it will continue to act, the bar being driven from one magnet to another with the velocity of two or three hundred vibrations in a minute.

Such an application of magnetism, however, we might despair of rendering effective for mechanical purposes, the power being small, and the mode of working inefficient.

* [And so, the case being reversed.-AM. ED.]

I have now, however, to state a method which has lately been discovered, of exciting magnetic power to a much greater degree than has ever been effected by the permanent or simple magnet, and in a way much more applicable to machinery. This consists in employing a voltaic battery,* generally of trifling power, by means of which magnetism may be generated in a bar of soft iron, by simply wrapping it with a lengthened coil of copper wire, previously covered with an envelope of silk or cotton thread, and then connecting the ends of the wire, one with. the copper, and the other with the zinc element of the battery. The bar is thus at once converted into an electromagnet, and possesses, so long as the communication continues, all the properties of a permanent one, the power generated increasing in proportion to the quantity of wire employed. With sixty feet of wire, for example, Professor Henry caused such a bar as we have described to raise seven pounds avoirdupois, but when the wire was increased to eight times the length, he found it to have acquired the amazing lifting power of six hundred and fifty pounds.

But that which renders the electro-magnet likely to become valuable as a moving power, depends chiefly on another principle. Unlike the permanent magnet, the polarity of its two ends results entirely from the connexion which the ends of the wire are made respectively to have with the copper or zinc of the battery; so that, as often as this communication is interrupted, the bar loses most of its magnetic properties, and when the connexion is reversed, a corresponding change takes place in the poles, -that becoming instantly north which formerly was south, and vice versa.

The mode of generating motion by such an agent will easily be understood by supposing a case. Let a horseshoe electro-magnet be fixed in a perpendicular position, with its poles pointing upwards, and let there be suspended over them a bar magnet. This bar will, of course,

*[The voltaic battery is an apparatus for the developement of galvanic electricity; and is so named from its inventor, the philosopher Volta.-AM. ED.]