The variable stars of these three classes are all marked by regular periods which recur with great precision in the case of the Algol and short-period stars, and with a less degree of precision in the case of those of long period. There are, however, in addition to these orderly bodies a number of stars whose variations present all degrees of irregularity, from sudden changes at uncertain intervals of time to a slow ebb or flow of light-giving power persisting in the same direction through years or even through centuries. Obviously no general law is applicable to bodies of such diverse characters.

One cause we may however postulate as a likely source of variation of an apparently lawless character, namely, the friction engendered by the passage of a moving star through a region of space occupied by nebulous matter. There is at all events good reason for believing that this is the compelling cause in the production of 'new' or temporary stars, bodies which in a sense may be regarded as variables with a single maximum. Such bodies have in all ages formed one of the most striking of celestial phenomena, and with them as in so many other cases it is only with the application of the spectroscope that real knowledge has come.

The first and most obvious explanation of the appearance of a new star, at a point in the heavens where none had previously existed, was the collision of two dark bodies with a resulting incandescence of the mass. Such an explanation is, however, negatived by the spectroscopic evidence, and, while there are still some doubtful points to be cleared up, it is now generally admitted that in the rush of a dark star into a cloud of nebula is to be found the kindling cause. If the nebula be not a homogeneous mass, more than one light maximum is possible, a supposition which coincides with the actual results of observation.

The occurrence of Nove from the lighting up of previously dark stars, and the fact, as we have already seen, that many bright stars are accompanied by invisible companions, shows us clearly that the visible stellar universe is interpenetrated by vast numbers of bodies, of star-like dimensions, emitting no appreciable light.

The subject of dark stars is one of extraordinary interest and importance, to which the apparent impossibility of obtaining any real knowledge of such bodies only serves as an added stimulus. As the inevitable progress of every radiating mass is to fall in temperature till it finally reaches that of the surrounding medium, we cannot doubt that the

ultimate fate of every star, unless rekindled by some chance encounter, is to become cold with the coldness of space. To what extent such chance encounters will tend, on the whole, to compensate for the slow and continuous heat dispersal we cannot say, but we can quite confidently assert that this compensation cannot be complete, or, in other words, that any aggregation of matter, however far extended and however vast the distances between the component units, must at some epoch assume the same temperature throughout. How far this progress has yet been traversed by our universe we can form no idea, but unless we assume, which we have no justification for doing, that it contains only bodies belonging to a limited period of evolutionary history, we are driven to the conclusion that the dead stars must outnumber the living ones by many, or it may be millions, to one.

Can such objects be brought within the power of our instruments, except in the case where they form one member of a binary system or return to incandescence as new stars?

As photographic records of the sky increase in number, and as the scrutiny to which they are subjected becomes more systematic and more searching, it is possible that cases where bright stars are accidentally obscured by darker ones, with which they have no gravitational connexion, may be observed. It must be confessed, however, that the chance of such an occurrence is very remote, and it is not in this direction that we must expect to open up a hopeful line of advance. Nor should we meet with better success were we to set ourselves to photograph a bright mass of nebula in the hope that some obscure body might interpose itself and advertise its presence on the photographic plate by showing as a dark spot on the bright background. No such result would follow. The subtraction of a single point of light from a luminous area would have no perceptible effect on the image of such an area at the focus of a lens or mirror, and, unless the object of which we are in pursuit be either vastly larger or much nearer to us than any bright star, its image would be sought in vain. The existence of bodies of the requisite dimensions or proximity presents no inherent impossibility. We can only say that they have not yet come within the range of our experience.

The search for dark stars not yet cold, utilising for the purpose the heat rays that they emit, is by no means a hopeless enterprise, and is one that we may expect to see undertaken in the not remote future. Two methods of research are available. We may measure the heat radia

tions at any selected part of the sky by the use of the bolometer or radio-micrometer, or, which seems the more practicable method, we may photograph the sky with plates made specially sensitive to the infra-red or heat rays. Such plates can be prepared, and their systematic use, with the aid of an adequate instrumental equipment, would not improbably yield results of considerable interest and importance.

By adequate instrument equipment we mean a telescope of very large aperture, and we are here brought up against a fence which often bars progress in astrophysical research, namely, the continued necessity for larger, and hence more costly, telescopes, with ever more intricate adjuncts, and, above all, the choice of the most favourable climate for the location of our observatories. This is somewhat disheartening, inasmuch as it appears to put the price of progress too exclusively on a mere monetary basis; but an examination of the most hopeful lines of advance will show that for the great majority of them an expensive instrumental outfit is the first necessity. That this should be the case when we are dealing with stars of an extreme degree of faintness, and still more when concerned with such elusive objects as stars emitting no light at all, is not surprising, but even with our own sun, where we might be inclined to think that an excess rather than a defect of light and heat is to be guarded against, future spectroscopic progress imperatively calls for telescopes of great light-grasping power.

The astrophysics of the future is, then, a science demanding gigantic telescopes, placed in situations selected for the purity of their atmospherical conditions, where the delicate radiations of heat and light that it is its business to study suffer the minimum amount of obstruction from dust and moisture.

It is to the credit of the American astronomers that they have long since recognised and acted upon this consideration, and have not hesitated to locate their telescopes remote from the conveniences of civilised-or perhaps we should say over-civilised-life, if thereby they might attain the inestimable advantage of a transparent and tranquil sky.

In this country we are not so fortunately placed, and it is impossible to obtain ideal conditions within the precincts of our islands. The high tableland of South Africa, however, offers almost exactly the atmosphere which is required, and it is earnestly to be hoped that in no long time some enlightened millionaire may come forward with an offer to

establish and endow a great physical observatory in one of our southern colonies, an institution which might compete in friendly rivalry with the famous foundations of Lick and Yerkes.

But while fully recognising the signal importance of the instrument and its position, we must never forget that the moving force of the observatory lies not in graduated circles, though of the most minute precision, nor in discs of glass, though fashioned in the most delicate curves, but in the brain and soul of the astronomer, and that, despite all the cunning of the instrument-maker, the man at 'the eye-end' still remains the paramount factor. The new astronomy ever presents fresh and complex problems which demand persistent work and the keenest intellects for their solution, and if it be objected that the results attained are remote from the practical affairs of life, and are incapable of any application to the useful arts, we may reply that so much the greater is the guarantee that its students will be pure searchers for truth.

ART. VI.-1. The Siege of Quebec and the Battle of the Plains of Abraham. By A. DOUGHTY in collaboration with G. W. PARMELEE. 6 vols. 4to. Quebec: 1901.

2. The Fight with France for North America. By A. G. BRADLEY. 8vo. London: Constable, 1900.

3. The Military Life of Field Marshal George, First Marquess Townshend. By Lt.-Colonel C. V. F. TowWNSHEND, C.B. 8vo. London: Murray, 1901.

THE

HE Conquest of Canada, a thing great in itself and leading directly to the revolt of the English colonies, is beyond all comparison the most important event in the English history of the eighteenth century; yet it has been curiously neglected by historical students, who have seemed to consider the squabbles of German princes and the campaigns of the Prussian king as of infinitely greater and more homely interest. People quote the saying of Pitt that he would conquer America in Germany, and yet fail to see that, so far as England was concerned, the origin, cause, and ultimate objective of the Seven Years' War was America. Some of our ablest writers have spent years in illustrating the campaigns and tactics of the Great Frederic; not one has given more than a passing mention to the really English quarrel which was being fought out, and, on the other side of the Atlantic, to the struggle which culminated on the plains of Abraham, not less than in Quiberon Bay, and which ended in the expulsion of the French from America, and in the foundation of the United States as an independent empire.

It is this, its final developement, which has given the long rivalry between England and France the peculiar interest which it has to Americans, and has led the historians of the United States to devote particular attention to it. It is to them that we have to turn for anything like a satisfactory history of the war, and in a more especial degree to the works of the late Francis Parkman, whose volumes on the growth, strength, and failure of the French dominion in North America are, and will continue to be, the principal source of our information. On the later phase, his 'Montcalm and Wolfe' must be reckoned as the classical authority; and though nearly twenty years have now elapsed since it was given to the public, there are but few points, and those of very little historical importance, on which later research can suggest any correction. Parkman,