seen a photograph of such a remarkable coincidence having occurred. So it seems to have happened in this instance, that two of the dark bodies in space have come together. They need not have been very large bodies. The probability is that they were not very large bodies. Also it is not necessary to suppose that they came actually square together. It may have been hardly a collision at all-a mere grazing collision. If they came excessively close it is conceivable that the blow would produce a tremendous amount of friction, and it would develop a considerable quantity of heat. It may be said, "Yes, but if they come together at a temperature so cold as that at which we know even air itself is a solid lump, is it conceivable that the mere knocking together of those two bodies can create a temperature so great as to render incandescent those vast bodies of hydrogen, whose light is radiated millions and millions of miles throughout the universe?" A few figures will show that it is conceivable this might take place.

I am not going to trouble you with more figures than are absolutely necessary. You remember that a rifle bullet when fired from a rifle and hitting a target, is warm when it is picked up. That warmth is due to its motion being stopped by the blow against the target. If a body moving at a velocity far faster than that of a rifle bullet strikes against another, the heat developed in that body would be greater still. Take a piece of coal and suppose it to be sent through space at a velocity of five miles a second-ten times the velocity of any bullet fired from a rifle, then that piece of coal, if it struck against a wall, or came into collision with another piece of coal travelling in the opposite direction, would develop from the blow as much heat as could be produced by the combustion of the coal itself. But these objects move at a pace far greater than five miles a second. This earth moves at a velocity of about four times that. A number of the stars move at a far greater velocity. It is certain that those bodies in the new star had speeds which may have amounted to hundreds of miles a second. Let us suppose it to be two hundred miles a second, which is not unreasonable. A body going at five miles a second has as much energy in virtue of its motion as an equal weight of coal would yield in perfect combustion, so that if it is going at two hundred miles a second, that means it has as much energy as sixteen hundred globes of coal of the same size. Imagine two such bodies meeting in space; the energy

produced by the collision of those two bodies is equivalent to the amount of heat produced, which is sixteen hundred times as great as all the heat that could be produced by the burning of two masses of coal as big as those two bodies.

Is it any wonder, then, that by such a collision a flash can be produced that carried its message throughout the whole extent of millions and millions of miles between where we are situated and where that incident took place? Such we believe to be the origin of this star. We are not left altogether to speculation in regard to it. There are many other confirmatory circumstances. In fact, remembering the myriads of such bodies that are there it is exceedingly likely that such a collision should occur, and that it should produce such an effect as we have seen. If any one doubts that a collision can produce such a glorious radiance they have only to look at the shooting stars. A shooting star is a brilliant streak of light. In one brief fraction of a second that little object is transformed by a temperature far greater than we could produce in our most powerful furnaces into heat. It can be shown that an object a child can carry would, if it were launched as a meteor dashing into our atmosphere, produce sufficient light to astonish a large part of the earth. It has been calculated that a meteor which appeared in America some months ago and was not heavier than a pound or so, produced so much light and heat by collision with the air, that the light was as great as could be produced by an electric engine driven by a 40,000 horsepower engine, and the noise that it made was as great as if that light were accompanied by music from fog-horns, blown by another 40,000 horses.

I must add a few words as to the process of evolution, so to speak, which we see going on around us in the heavens. This subject has come very much before the attention of astronomers lately in consequence of discoveries that have recently been made. One of the greatest of philosophers, Immanuel Kant, laid the foundation of that remarkable nebular theory which ordinarily goes by the name of Laplace. Had Laplace and Sir William Herschel lived to these days, they would have heard with unbounded interest of the development of our knowledge which has arisen from photography. Here is another point in the heavens, and here is some trace of the nebulous material—this glowing

*Pointing to the screen.

material which Kant imagined-for in his days they could hardly have known much of its existence.

What I want you to look at in this picture is the faint diffused light-light not from a solid material-not from the stars at a distance, but light from incandescent gas. In this picture we have instances of nebula which are chaotic, and here you see nebula in strange wisps. You might think they were little bits of cloud in the sky; but they are there, night after night, hardly to be seen with the aid of the best telescope.

There we have one of the great glories of the heavensthe great nebula in Orion, this being the famous picture taken by Dr. Isaac Roberts, and here we have parts of it above and below extending to a vast distance. [Exhibiting on the screen.] In this we have the nebulous gaseous material, as it were, drawing itself into shape.

Now we will look at another. This is the famous "Dumbbell Nebula." This gives an astonishing illustration of the possibilities of the photographic plate. It has a patience and delicacy that no human eye possesses.

Now we come to another-the "Crab Nebula," as it is called. I have shown this with the view of illustrating as it were the varieties of these nebulæ. We may look at different trees in a forest-the old veteran that weathers the centuries, and then we come down gradually to the little sapling until we come to the little acorn just sprouting. We can read the history of the oak by looking at individuals in the forest. So we try to learn what nebulæ have to tell us by their structure as to the history of the individual objects. But here is a form still more advanced. [Exhibiting on the screen.] Here we have a photograph of one of the most interesting subjects in the universe. That is the great spiral nebula. You can magnify it, and it will bear the test that it ought to stand. It was taken by Mr. W. E. Wilson, in Ireland-a most accomplished astronomical photographer, and I ask you to observe in this that sort of evolution that Laplace explains. Parts of it tend to form what may in all probability be the planets that are ultimately to attend on that sun in the centre. You see here indications of the direction in which the rotation proceeds. They are all moving round the same way. We see this planetary system lying near the same plane, and now there is an astonishing fact that I have to state. Here is another spiral taken by Dr. Roberts. We look at this with more interest

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because in it we are looking at an object that no human eye has ever seen. The photographic plate sees it but we do not. The late Professor Keeler commenced a survey of the heavens. He took a square degree here, and one here. He took, if I may use the expression, samples of the heavens on photographic plates. On one of those plates he found three new nebule; on another ten; on another twenty, and on another even as many as thirty--not less than three on any one. If he were to photograph the whole heavens he would want 40,000 plates. He had only taken a dozen or so, and had not found fewer than three on any one, and ten times that number on some. If there were three new nebulæ at least on each of those 40,000 plates, that means 120,000 new nebulæ in the heavens. There is an astonishing fact to be added, and that is, of these more than one-half are spirals-hence spiral nebulæ assume great importance in the celestial economy.

Here is the last one we shall look at. It was taken by Dr. Roberts, and is generally believed to be the most remarkable astronomical photograph ever taken. It is a picture of the great nebula in Andromeda. If it could have been turned into a better position we should have found another great spiral.

These pictures show how the theory suggested by Kant and developed by Laplace is borne out in the most astonishing manner by these more recent observations with photography.

My lecture is at an end. I began with a statement of the origin, so far as we are able to discover it, of these stars which occasionally and suddenly burst into view.

I have shown how those stars arise from a collision, and I have tried to show how by a contraction of a nebula, as most of us believe, the great sun that we know in heaven came into being with its planets.

The whole tendency of modern science so far as we have been able to understand it, has been to show that what Kant and Laplace and Herschel laid down is, in the main, the actual order of events that has taken place in nature. In concluding my lecture to this Institute, where it has given me such pleasure to appear, I cannot help saying that the more we study these things, the greater is the mass of difficulties, which seem to us insuperable if we try to unravel them by the light of science alone. It is true, we believe-I myself certainly do that our solar system has originated

from the nebula, just as I believe the adult came from the child; but if you ask me where that nebula came from?— well, we may say it came from the collision of two stars. But then comes the question, "Where did the two stars come from?" To that science really gives no answer; and as far as I can understand these things, the very circumstance of the heavens seem to me to bear written on them the impress of the fact that they cannot have gone on from all time as they are now. There must have been, so far as we can understand it, some beginning-some time at which there was an intervention of force and action such as science is not able to take cognizance of. Hence it is I cannot but express hearty sympathy with the efforts, and successful efforts, which have been made by this Institute to show that in our endeavours to understand the wonders of nature, we have ever brought before us the fact that there are innumerable mysteries in nature which can never be accounted for by the operations with which science makes us familiar, but which demands the intervention of some Higher Power than anything that man's intellect can comprehend. [Loud applause.]

The PRESIDENT.-Ladies and gentlemen, I am sure you will agree with me that we ought to pass a hearty vote of thanks to Sir Robert Ball for this most interesting and most suggestive lecture that we have just heard. Perhaps it is not quite usual to propose a vote of thanks from the chair, but in the absence of Sir Joseph Fayrer, who has been obliged to leave, and who had undertaken to move the vote of thanks, I have great pleasure in doing so. (Applause.)

I need not occupy your time-in fact, it has been so delightfully occupied during the whole of this lecture, that anything I could say now would only be coming down from a ladder. Perhaps some one here will have the goodness to second this resolution.

Dr. WALTER KIDD, F.Z.S.-I beg to second the vote of thanks to Sir Robert Ball for his valuable lecture.

[The resolution was then put and carried with acclamation.] The SECRETARY. I wish to be permitted to add one word to the thanks that have been accorded to my distinguished friend-a

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