millions" of years for its formation, and assuming his principle of contrasting time and space, may we not ask him in return, What was the structure of the primitive Earth? What were the periods of time required for the deposition of each formation? And of what use was an arrangement requiring myriads of millions of years for its completion ?

Believing that "nebulæ are vast masses of incoherent, or gaseous matter, of immense tenuity, and destitute of solid moving bodies," a theory which he derives from another theory called the nebular hypothesis, without adducing the least trace of evidence in its support, our author boasts, not surely in the spirit of the inductive philosophy, that he seems to have made it CERTAIN that the celestial objects (the nebula) are not inhabited. To this we reply, that we have made it MORE PROBABLE that the CELESTIAL objects are inhabited,-an assertion less presumptuous, but more certain than his.

We have described in a preceding chapter the spiral nebula discovered by Lord Rosse, and we have endeavoured to explain the appearance of motion, which may be considered

as indicated by the spirals which they exhibit. With his accustomed boldness, and extravagance of speculation, our Essayist has made the following observations on these spiral forms: The comet of Encke," he affirms, "describes

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a spiral gradually converging to the Sun," and in 30,000 years this comet will complete its spiral, and be absorbed in the central mass.

But this spiral converging to its pole so slowly that it reaches it only after forming 10,000 circuits (or spirals,") while “ there are at most three or more circular or oval sweeps in each spiral (of the nebula), or even the spiral reaches the centre before it has completed a single revolution round it." From data like these, the following theory of the spiral nebulæ is deduced:" If we suppose the comet (that of Encke) to consist of a luminous mass, or a string of masses, which would occupy a considerable arch of such an orbit, the orbit would be marked by a track of light as an oval spiral, or if such a comet were to separate into two portions, as we have, with our own eyes, recently seen Biela's Comet do, or into a greater number; then these portions would be distributed

along such a spiral. And if we suppose a large mass of cometic matter thus to move in a highly resisting medium, and to consist of patches of different densities, then some would move faster, and some more slowly, but all in spirals, such as have been spoken of, and the general aspect produced would be that of the Spiral Nebulæ, which I have endeavoured to describe." A hypothesis more wild and gratuitous than this was never before submitted to the scientific world. In what part of the nebula do the cometic patches reside before they begin their motion of descent to the nucleus; and what is the cause of their quitting their place of rest? No comet out of the many hundreds that have been observed, has been so negligent of its tail as to leave it behind. Encke's Comet has been equally careful of its appendage, and the division of Biela's Comet was only apparent. But even if a comet were to separate into a number of portions, these portions would, like the division of Biela's Comet, travel along with it and again unite themselves into one, so that the analogy of this comet is destructive of the speculation which it is brought to support.

CHAPTER XIII.

OBJECTIONS FROM THE NATURE OF THE FIXED STARS AND BINARY SYSTEMS.

HAVING, as our author congratulates himself, "cleared away the supposed inhabitants from the outskirts of creation, so far as the nebulæ are the outskirts of creation," he proceeds to consider the fixed stars, and examine any evidence which he may be able to discover as to the probability of their containing in themselves, or in their accompanying bodies, as planets, inhabitants of any kind. We have already stated the grounds upon which the most distinguished astronomers have believed that single and double stars are accompanied with planets similar to our own; and we shall now consider the objections which are made to this opinion.

Beginning with clusters of stars, the author whose opinions we have been controverting, justly observes, that they are in the same. category with resolvable nebulæ, and he therefore regards it as "a very bold assumption to assume, without any farther proof, that these bright points are suns, distant from each other as far as we are from the nearest stars. When these clusters are globular, Sir John Herschel regards their form as "indicating the existence of some general bond of union in the nature of an attractive force;" and assuming that the "globular space may be filled with equal stars, uniformly dispersed through it, and very numerous, each of them attracting every other with a force inversely as the square of the distance,

each star would describe a perfect ellipse about the common centre of gravity as its centre," Sir John therefore conceives that "such a system might subsist, and realize in a great measure that abstract and ideal harmony which Newton has shewn to characterize a law of force directly as the distance."

Referring to this ingenious theory of globular clusters, the Essayist illustrates it by asserting,