It is generally accepted by chemists, that there are vacuous spaces between the atoms of a molecule or particle, and that the atoms composing a solid body are in ceaseless motion.

The medium for the transmission of light has been shown by Sir J. Thompson to possess the properties of an elastic solid. As radiant heat and light are identical, the same medium must serve for the transmission of heat. "Professor Clerk Maxwell maintains that light, electricity, and magnetism are all affections of one and the same medium; that light is an electro-magnetic phenomenon, and that its laws can be deduced from those of electricity and magnetism."—(Deschanel.)

Mr. Lockyer, about the beginning of the year, in his celebrated experiment, has shown that some chemical elements may be transformed into others, which indicates the possibility of all the chemical elements being resolvable into one.

Mr. Crook, at the Royal Institution, March 5th, this year, has shown by experiments in high vacua, in which tubes were exhausted to the millioneth of an atmosphere, that matter may be in a fourth state—an ultra-gaseous state.

The object of the present Essay is briefly to show, (1) that the transmission of light and electricity is in the nature of a percussion; (2) that the suns, of which a stellar system or aggregation is composed, require an expansive force to keep them asunder; (3) that the mode of action of the gravitory force must be similar to that of a current, but that it cannot be a current, and that the gravitory force may be a motion of attenuated matter; (4) and that the action of this matter may produce the same effects as a gas in a similar way.

Light and Electricity a Percusssive Phenomena.

The undulatory theory of light is now an established belief.

It is desirable to have as good an idea as possible of the conditions necessary to allow of so stupendous a velocity as that which light has.

Reaumur, from observations of the eclipses of Jupiter's satellites; Bradley, in explanation of the aberration of light; Fizeau, by means of reflection and a rapidly-revolving toothed wheel; and Foucault, by means of the revolving mirror, have shown the velocity of light to be about 186,000 miles per second.

It is just as well perhaps to note, that while the velocity of electricity is believed to be the same as that of light, that Wheatstone found the velocity of electricity, in a short wire, to be 288,000 miles per second, while, in the Atlantic cable, it is, owing to resistance, only about 1,500 miles per second.

When it is said, therefore, that light is perceived, it would simply mean that the luminiferous tether in the eye was put in motion. When it is said that, by means of a lens, objects are burned, it is meant that the æther was put in intense motion at the focus. If, therefore, a spark is struck at a distance, nothing has come actually from the spark to the eye. A jar was given to the æther by the spark, and the æther, acting like a solid, instantly transmitted this jar to the æther in the eye. If this æther is theoretically solid, it can only be of the same density throughout, whether at the sun or in the far regions of space. This, however, seems improbable. This æther is easily displaced. Might there not, if necessary, be some element, along with the luminiferous æther, filling space? This other element might be capable of contraction and expansion in a high degree.

A few brief facts about the great comet of 1843, from Sir John Herschel's "Outlines of Astronomy," will show the extreme tenuity of whatever this substance is which pervades space, and that this substance acts like a solid:—"The tail of the great comet was from 50 to 60 degrees in length, and the head and nucleus appeared with extraordinary splendour. It approached within 60,000 miles of the sun's surface, and was subjected to a heat 47,000 times greater than that which the sun showers upon our earth—a heat 3½ times that which will melt rock crystal. The comet swept round the perihelion segment of its orbit in two hours, at the rate of considerably over 300 miles per second." Sir John Herschel remarks generally on comets:—"In no respects is the question as to the materiality of the tail more forcibly pressed on us for consideration than in that of the enormous sweep which it makes round the sun in perihelio, in the manner of a straight and rigid rod, in defiance of the law of gravitation, nay, even of the received laws of motion, extending (as we have seen in the comets of 1680 and 1843) from near the sun's surface to the earth's orbit, and yet whirled round unbroken; in the latter case through an angle of 180 degrees, in little more than two hours. It seems utterly incredible in such a case that it is one and the same material object which is brandished. If there could be conceived such a thing as a negative shadow—a momentary impression made upon the luminiferous æther—this would represent in some degree the conception such a phenomenon irresistibly calls up."

How extremely attenuated must the æther be to allow of so enormous a velocity as 866 miles per second! But this stream of light, shooting from a comet called its tail, which is always directed from the page 5 sun, what is it? How is it caused? If part of the comet were composed of the luminiferous æther, or matter in that form, and this æther were occluded within an envelope of other matter, it could be conceived that this æther was rapidly set free by the heat of the sun melting off its covering—an outward movement of a tubular or conical portion of the luminiferous æther from the body of the comet would result. There would, therefore, be a kind of friction at the edges, which, if an electrical phenomenon, would be visible, and it might even he explained optically. The undulatory theory requires—a percussive transmission requires—a medium of great power and extreme tenuity. Does not gravitation require as well a powerful though attenuated agent?

How are Suns kept apart?

On a fine night at any time of the year stars, or distant suns, are seen in every direction around, they are very thick in the milky way. There are about 6,000 visible to the naked eye, and the number of stars perceivable in the most powerful telescope is estimated at 20,000,000. The universe or stellar system of which the sun is an individual, is supposed to be ring-shaped; separated from this universe by vast immensities of space, are perceived other universes or stellar systems, these are of all sizes, shapes and brightness, they have many varied forms—spiral, elliptical, and spherical. Mr. Proctor, however, considers the stellar system as continuous to a telescopic extent; in any case, however, there are aggregations and clusters.

Sir John Herschel seems to wish that the law of gravity may hold good as in the case of a planetary system, for he thinks the supposition that these star systems have an axis of rotation will be needless if the system is of a regular spherical form. In this latter case he thinks the stability of such a system is dynamically possible, without supposing the governing force to be other than that of gravity so acting.

Herbert Spencer's opinion will probably indicate the belief of a large section of writers on this subject. In "First Principles" he indicates that the only governing force is gravity, causing a closer aggregation, which is kept in check by the motion of the suns. In explanation of this point, Maedlar conceived a central sun, which he placed in the Pleiades, this central sun, however, is not considered probable. All these opinions indicate a general belief that gravitation draws suns as well as planets together, and that a centrifugal force, or some kind of motion is necessary to keep them apart. Time and distance might explain much, but principles should be satisfied. The law of gravity has been verified in every way in the solar system, and seems to prevail in the case of double stars. In both these instances, however, the destruction of the system is directly counteracted by centrifugal motion or force. All the planets of the solar system revolve in one plane round the sun. Comets are held to be of an exceptional character. Pallas departs considerably from the ecliptic plane, but will probably not be held to overstep allowable limits. If planets were revolving round the sun vertically to the ecliptic plane, the page 6 planets in the ecliptic plane would draw those that were out of it towards that plane, as there would be no counteracting force, and eventually the planets would all revolve in some common intermediate plane.

The consideration of the stability of a stellar system, cluster, or aggregation can now with advantage be entered upon. From the centre of such a system many suns would be seen circling in an imaginary horizontal plane, many in a vertical plane, and a vast number in intermediate planes. Take the case of two suns revolving in an imaginary horizontal plane. They must be exactly opposite, or they will have their actions mutually accelerated or retarded, till they either formed one sun or the equivalent to a planet and its satelliate. These two suns could have been imagined exactly opposite, but a third sun can be supposed to move in a plane vertical to theirs. If the two first suns A and B are exactly in the east and west points, the third sun C can be imagined at the zeinth. C exerts by the force of gravity a pull on A and B at right angles to the directions of their motions. There is no counteracting force here, consequently the three suns begin to take directions towards moving in one plane. There could have been imagined a fourth sun D at the nadir to counteract the pull exerted by the third sun, and there would then be an equilibrium of forces. The suns, however, proceed in their orbits, and when one-eighth of their orbits have been described it will be seen that the equilibrium of forces has been overthrown. If A is in the north-east point, B will be in the south-west, while C may be supposed to be half-way between the nadir and the west point; C is now found to be nearer to B than to A, and consequently the stability of the system is destroyed.

With all intermediate planes it is still more manifest that there cannot be equilibrium for more than an instant. The action of gravity causes all bodies to move in one plane as in the solar system. It follows from this that there is some mode of action of gravity between sun and sun different to that holding good between planets and their centre of attraction. Possibly there might be some force emanating from the sun as a product of its intense heat tending to keep suns apart. It might be that there is some fluid, as the electric fluid, evolved by the suns which, flowing out from the suns, overpower the weakened force of gravity at a remote distance. Or it may be that there is no peculiar emanation from suns, in which case it might be that a solar system tends to separate from other solar systems in the same way that the molecules, or atoms of a gas, move from one another, and diffuse themselves as widely as possible through the space they occupy.

Any system, therefore, that has gravitation for its governing force will have a single plane in which its members move. As stellar systems are not of a plane form, gravitation is either not the ruling power in them, or it does not act between sun and sun, as it does between the members of the solar system.

The Mode of Action of the Gravitory Force.

A leading writer on astronomical subjects, says that though nearly equally divided, the balance of opinion slightly inclines in favour of the force of gravity acting simply as a property of matter, and that no agent is intermediately concerned in drawing one mass of matter towards another. Any theory that might have formed, seems to have been of value only in a negative sense, in that it was less objectionable than some other. If the way in which the force of gravity must act be considered, many great difficulties will present themselves.

If that power which causes bodies to gravitate be exercised through the medium of a current, then a current must be conceived to flow from an indefinite distance outside a body, and towards the centre of that body. This current, of course, becomes more condensed as it approaches the centre, and this would be in agreement with the facts of the gravitory force.

The motion of a current in itself would be a sufficient cause in carrying one body towards another. Several instances, however, present themselves to the mind which render the supposition that the force of gravity is a current impossible, or almost impossible. In considering the mutual gravitation of the earth and moon, a current would have to be conceived flowing towards the centre of the moon, carrying the earth with it; and at the same time there must be conceived a contrary, and consequently opposing current, flowing towards the centre of the earth and carrying the moon with it. The currents oppose each other, and the supposition, therefore, is opposed to reason.

Though, however, gravitation is not the effect of a current, yet, if a single current only were to act it would give a partially satisfactory explanation of gravitation. Whatever agent or medium causes gravitation must do the work of a current, but must remain in the same place. It must, therefore, have a peculiar (perhaps a kind of vortical) motion of an intensely rapid kind. The motion might be of an endless screw character. In any case in its effect it must act upon matter, as the webbed foot of a swimming bird acts upon the water.

Though not a current, the force of gravity acts like one. For the sake of simplicity it would be well to suppose that it is a current. If a plank is pushed endways against a stream of water, it can be so pushed without any great labour. It would be a matter of greater difficulty to hold the plank transverse to and against the stream when its edge was presented. If the plank were held transverse with its face against the current, the difficulty of holding it would be very much greater. If, however, the plank is held against the force of gravity, imagined as a current, it will make no difference whether the plank is held end, edge, or face up. That is, the power required to maintain the plank against a current of water is very different in three cases; but, to sustain the plank against the imagined current of gravity, exactly the same power appreciably is required in the three cases. A little consideration would show clearly that only the outside of the plank was acted upon by the current of water, while the supposed page 8 current of gravity must act on every particle of the plank. The current of gravity must then flow through the solid as water flows through a sieve. As an illustration of the principle of the action of gravity, the case may be taken of a ship in which the sails are not made of canvas, but of a kind of netting. The wind rushes through these sails of netting, but the ship is driven forward nevertheless. That the force of gravity (if a current power) acts upon matter as the wind acts in the foregoing case on every thread of the sails, will be considered possible or even necessary.

At the surface of the earth, the velocity produced by the force of gravity is, at the end of one second, 82.2 feet; at the end of three seconds, 96.6 feet, &c. The question now arises, whether there is any limit to this velocity. This point has not perhaps been directly tested, and it cannot be easily answered. The ultimate velocity that could be produced by the gravitory force of the sun is reckoned to be 400 miles per second. Another question also arises. Will a mass, say, of iron weigh as much as the same volume and density when cut into many small pieces? No experiments have probably been made on this point either. Another point presents more difficulties. The motion of the gravitory fluid within the mass having been lessened, the more rapidly moving, or gravitory matter, outside the mass, presses inwards to restore equality of motion; but whether the slower moving is driven out of the mass, or excited to almost equal activity, is difficult to determine. This is a most important point in considering the action of the gravitory fluid among the particles of a solid so vast as that of a planet.

Some possible results are: that the motion of particles of gravitory matter is greatly destroyed, and that the particles of a solid are put into motion to some slight extent.

The conception of what an element of matter might be is most important. This element of matter has to satisfy so many conditions that it is difficult to conceive it.

Perhaps the element described in the following lines would satisfy many of the conditions which have to be fulfilled:—It may be considered as having the form of a life-buoy, with the opening or inner circumference, however, narrowed down to almost nothing. The tubular portion must be considered as a hollow shell—a thin elastic tubular film. The tube must be considered as revolving within itself, so to speak, the inner part having a motion upwards, and the outer a motion downwards. To aid the imagination, this tube may be supposed to consist of very elastic rings laterally compressible, and expansible in a very high degree. They can be considered as gummed together at their edges. If, now, a tight-fitting rod is pushed up through the opening or inner circle of this tubular series of rings, all the rings of which the tube is composed will of course revolve—the inner part of their circumference moving upwards, and the "outer parts of their circumference moving downwards. The general outward form of this element may be supposed to be nearly spherical. It may be likened to a slightly- page 9 flattened orange, with a small cylindrical portion cut out around the vertical diameter, the top and bottom of which tube would be slightly funnel-shaped. The motion would then be the same as if the rind of the orange moved downwards, ascended through the funnel-shaped tube, and so kept circulating. In any space these elements would occupy positions similar to those occupied by equal-sized oranges packed in a box. Their axial diameters are supposed to be vertical. It should then be remembered that all the outsides of these oranges have a motion downwards, the ascending motion taking place through the opening cut around what might be called their polar diameter. A little consideration will now show that all these elements exert a mutual pressure; that they always set their polar diameter perpendicular to a flat surface; that the contiguous elements adjust themselves; that any inert substance is carried downwards; that an element of slower motion is carried down wards, while an element with quicker motion will raise itself upwards, and that they will possess other powers or properties besides.

The Relative Density, Work, and heat-equivalent of Work of the supposed Gravity Matter or Æther.

Matter has lately been found to be in all states, it has been long know to take three forms, the solid, liquid, and gaseous; in addition to these states, however, solids are known to take a spongy or viscid state. Iron is neither solid nor liquid just below the melting point. Doctor Andrews and others have shewn that there is a state of matter intermediate between that of liquid and gas. Mr. Crookes has indicated that matter may be in an ultra-gaseous state. There is no want of continuity, the matter which is in the state of an extremely attenuated gas, may therefore, be reduced by pressure and cooling to the condition of a solid. The consideration of recent discoveries in chemistry—or of the most recent chemical views—especially in connection with solution and dissocation, indicate that physical and chemical action are continuous. There is no line of demarcation between the two kinds of action, heat alone will produce of itself a vast number of chemical effects, chemical action may therefore be taken as one extreme of physical action. All laws of chemical action are founded on the hypothesis, that the atoms of matter are in perpetual motion, this motion being in the case of gases of an astoundingly rapid character.

The known effect and nature of gravitation are not adverse to the conception that planets, and perhaps suns, are the production of that by which they are environed—the greater the body the greater the power required to produce it. The gravitory force may be supposed to be the motion of matter in that elementary state in which it is diffused throughout space. This matter, together with perhaps some other kind, must be assumed to be the medium by which light and electricity are transmitted. This matter might have much the same land of motion as the chemical elements in their gaseous state. The motion of this matter as it came in contact with solid bodies would be retarded, and condensation of the matter would follow.

Sir John Herschel has shown in a discussion on atoms, that the æther must have vacuous spaces. It would be well now to consider the comparative condensations of this matter as it may be supposed to be indicated by the force of gravity.

For a unit of comparison, a mass of iron weighing one ton at the surface of the earth may be taken. At the surface of the sun this same mass of iron would weigh 27.9 tons, say 28 tons. It will save very tedious calculations to take the diameter of the sun at 880,000 miles, and the mean distances of the planets from the sun in round numbers.

The gravitory force of the earth on a body at a distance of 164,000 miles (at right angles to the edge of the plane of its orbit) is just equal to that of the sun on that body. It follows from this that as the moon is distant 240,000 miles from the earth, the sun's power in attracting the moon is 2½ times that of the earth.

If there be a gravitory fluid, then its comparative density at any point is known. In this it is similar to the atomic weights, or equivalents of the chemical elements. The weight of an atom is not known. The question is to say, what a certain volume of this supposed gravitory fluid would weigh. As it is the motion of this fluid which gives weight to all bodies, it cannot be directly weighed. As in the case of the planets, however, its weight or mass may possibly be arrived at.

If this supposed gravitory matter, which causes bodies to move, has its own motion destroyed by contact with a solid and immovable body, heat will be produced. It will perhaps be considered desirable, in one or two important cases, to calculate the amount of work done, or heat evolved, by the motion or destruction of motion of the elements of the gravitory matter. The gravitative power of the sun will in one hour deflect the earth from its tangential course about 8,483 feet. The gravitative force exerted by the sun upon the earth is only .00059949617 of the force of gravity at the earth's surface. It would take 5.5 worlds of water to equal the mass of the earth. The weight, so to speak, lifted by the gravitory force of the sun, would be, there- page 11 fore, .003297229 of that of a world of water the size of the earth. And the heat equivalent of the work done by the sun in deflecting the earth during one hour, would add to a world of water the size of the earth, a heat of-03523 degrees Fahrenheit. This is the heat-equiva-lent of the hourly work done by the sun in deflecting the earth. If the force of gravity at the sun's surface were the same as at the earth's orbit, and the sun's surface were completely covered by worlds of the same mass and size as the earth, the sun would deflect every one of them from their tangential courses (being supposed that they could all freely move) as much per hour as it did that of the earth in its orbit. It would take 47,578 worlds the size of the earth to completely cover the surface of the sun. The power of gravity at the sun's surface is actually, however, 47,413 times its gravitative power over the earth in its orbit. Consequently, the heat-equivalent of the work that could be done by the actual total power of gravity of the sun at its surface, would be sufficient to heat 79,472,390 worlds of water one degree Fahrenheit. The mass of the sun is equal to 1,903,019 worlds of water the size of the earth. This mass of water, equalling the sun, would consequently be heated 41.748 deg. Fall, per hour. The heat thus calculated for the sun would be 1,185 times that of the earth. There is this remarkable difference, however, between the two cases: In that of the earth, the gravitative power of the sun deflects the earth, and therefore does work, and no heat is evolved. In the case of the sun, the gravitory elements, if the same principle is similarly applied, do no work, motion is destroyed, and heat is evolved. Actually, however, the case must be a little modified. By heat must be meant the molecular motion of matter, solid, liquid, or gaseous; and by heat-equivalent is not meant heat actually produced but producible, and perhaps produced to a great extent.

The gaseous matter, which by its motion causes gravitation, must be conceived to act like a current, though it is not one. In its effect, the action of this gravitory matter on a body circulating round another is very different to that which it produces on the central body round which the secondary body circulates. Every body is subject to the direct action of its gravitory matter. The action of this gaseous matter will be the same as if it were a current rushing into the surface of that body. The atoms of a gas are supposed to be perfectly elastic—to be ceaselessly in rapid motion—and when occupying the same space their motion is not supposed to be destroyed, though it may vary with the temperature. Some gases are extremely difficult to solidify. What the action, therefore, of the gravitory gaseous matter on a solid, and the reaction of the solid on the gas, would be, is very uncertain. It is certain, however, that this gas must permeate all solids little or much, and it is very probable that, by its action on solids, heat would be evolved. As solids and liquids absorb gases, it is also likely that a portion of this gas would be reduced to the solid state. The extent to which this gravitory matter permeates the crust of a planet, the amount of heat evolved, and the quantity solidified, if any, is most page 12 indefinite. It will, nevertheless, be very desirable to know the amount of heat imparted to the crust of the sun or earth, on the supposition that the motion of the gravitory matter is completely destroyed and transformed into heat.

The outer crust of the sun, to the depth of one mile, has nine times the cubic contents of the earth, and to the depth of ten miles ninety times the cubic contents of the earth. The mass of water which is equal to the sun's crust ten miles deep could be heated by the total actual gravitory power of the sun 638,775 deg. Fall, per hour. If the sun's crust be taken to the depth of 100 miles, its equivalent of water would be heated per hour 63,877 deg. Fall., and so on. As the action of gravity at the earth's surface is one twenty-eighth of what it is at the surface of the sun, while the density of the earth is 5£ times that of water, the mass of water equivalent to the earth's crust to the depth of ten miles would be heated 4,148 deg. Fall, per hour. If 100 miles in depth of the earth's crust be similarly taken, the heat equivalent would be 415 deg. Fall, per hour. These calculations must be qualified to an extremely large extent by the considerations which have been previously noticed. There is again, however, a marked difference between the sun and the earth; the sun is comparatively almost stationary and its heat is conserved, while the earth rushes through cold regions of space, and radiates its heat very rapidly.

The one great conclusion that can be drawn here is that all bodies may be heated by the destruction of the motion of a material substance (if any) which causes gravitation, and the greater the force of gravity the greater the heat.