No. 11.

On the Origin of the Visible Universe.

That the visible universe is not a mere chance distribution is evident to the naked eye. But the probabilities of a definite order increases enormously with telescopic observation. Undoubtedly it consists roughly of a ring or disk of stars, which are so arranged on the celestial sphere that a great circle almost exactly divides it. Within this disk, Herschel tells us, there are roughly eighteen million stars, visible with his telescope. In the rest of the heavens there are two millions. Procter tells us this zone covers one-tenth of the celestial sphere, and shows that this great number is due more to distribution than to extension. How enormous thus is the aggregation of stars in the milky way. Again, Procter shows us that at the two poles of this ring, and covering a large arc, there are enormous aggregations of nebulæ, and that there are two almost completely clear zones on each side of the milky way. Again, in the same work, Procter uses a chart prepared by Sidney Waters showing star clusters and nebulæ. A large number of these clusters are arranged in a narrow zone which is even more strikingly approximate to a great circle of the sphere than is the milky way itself, and the two great circles are identical. Again, almost all the temporary and variable stars have been seen in the milky way. The page 12 revelations of the spectroscope, and the analyses of all the meteorites which have been examined, demonstrate that the whole stellar universe is identical in composition. These are the broader generalisations, and to me they are so striking as to render it almost a certainty that the visible universe is a system of tome kind having a common origin.

An hypothesis, which appears to account for such a system as our universe has been shown to be, is that it has been produced by the indirect collision of two stupendous bodies in space—bodies which probably rotated, and which carried with them a large number of smaller masses rotating around them in all directions. The collision was probably one in which the ratio coming into impact was not a very email fraction of the total mass. We have thus three masses to consider, which may be considered in two sections:—1st. The escaping pieces; and 2ndly, the coalesced mass. Unless we assume a stupendous independent velocity, it is certain that these escaping pieces will not pass away from the general attraction, The temperature of these bodies will not be very much increased by the collision, at least nothing compared to that developed in the coalesced parte. It is extremely likely that they would break up into many pieces. Generally these non colliding parts will have a higher velocity than any other pan, certainly they will at first. Secondly, of the coalesced parts. In a portion of these the momentum will be balanced, and here, of course, all motion will be converted into heat. This portion will be the hottest, and will tend to occupy the centre of the mars. In all parts where the momemtum is not balanced, a residual motion tending to rotation will be left. I have already shown how at first such a mass tends to take a spindle shape, and the whole of the material tends to occupy the plane which contains the line of mean direction of motion of the bodies at impact, and also the line joining their centres of gravity. This will be the ecliptic of the milky way. By following all the motions and attractions that the ends of this spindle are subject to, it will not be difficult for physicists to see how such stars as 1830 Groombridge may have been formed, of course, not at the origin of this galaxy, tut at the birth of other systems. Doubtless, from various causes, already discussed in former letters, a very large number of fragments will completely escape; but the chief part will remain in the system, probably forming the star cluster, star dust, and some of the stars of the milky way. But the still hotter parts at the centre of the entire mass, where the molar motion is more completely destroyed, will develop into an enormous nebula having a strong rotary motion, producing a lenticular nebula in which the circumference is, of course, cooler than the axial part, it having more residual molar motion of rotation. The general molecular velocity of the whole, were it uniform, would doubtless be sufficient to take the whole from the centre, but the molecular action, which I have called "selective escape," would probably cause a large central body to remain; the remainder would form a hollow spheroid, which would probably separats into a ring, and would follow the stars, and into two saucer shaped masses which would be carried by their own radial molecular velocity away to the poles, tending slowly from many causes to aggregate into groups. But it is not improbable that with great telespectroscopic power it may be found that the whole of the poles of the milky way may be found to be nebular. It will not be difficult to any physicist who may have read my paper on temporary and variable stars to see why most of these stars are in the milky way, nor why the space about our sun appears to be somewhat sparsely spread, nor why all the stars have en apparently undefined proper motion. It would tell much in favour of this hypothesis if, when the actual proper motions of a number of the stars are known (both the spectroscopic and angular component), if the resultant of these motions were distinctly more in the plane of the milky way than at right angles to it; for clearly, if this disc or ring were formed by aggregation towards this plane, it appears certain that most of these motions would be at right angles to it. In Procter's map of these motions, in the northern part of the milky way, the motion distinctly appears to be in the plane of the ring, but of course this does not give the spectroscopic resultant, Again it does not seem difficult to see why groups of stars have a commons direction in space, nor why stars appear in streams at slight angles to the milky way, as the whole of these conclusions seem to follow readily as general deductions from partial impact.

In my next letter I propose to discuss the available energy, in such a case of impact as I have described. This letter is longer than I desired, but I need not say that the full discussion of this question needs a volume. I have simply hinted at the mode of discussing it.