12 THE BODIES OF SPACE, 



thesis. The discoverer points to an imaginary space extend- 

 ing in each direction from the orbit of each planet, at the outer 

 limits of which its attractive power ceases and that of its 

 neighbour commences. This expanded orbitual space he calls 

 the planet's Sphere of Attraction. He has found in the 

 spheres of attraction the periods of the rotations of the several 

 planets : " the SQUARE of the number of times that each planet 

 rotates during one Revolution in its orbit, is proportional to the 

 CUBE of the breadth or diameter of its Sphere of Attraction." 

 This law, flowing out of a combination of the most important 

 elements of the system, namely, the relative distances and at- 

 tractive weights of the several orbs, "virtually tells us," says 

 Professor Nichol, " that the rotation of each planet is not a, 

 separate or isolated attribute, but a consequence of the relations 

 of that planet, in all its habitudes, with the general mechanism 

 of the si/stem; and thus it impresses a view of that system, 

 analogous in every important respect to that which charac- 

 terizes the philosophic speculation of Laplace. I hail it there- 

 fore as a virtual confirmation of that order of speculations, as 

 well as an eminent positive discovery." 



The Laplacian hypothesis, it will be observed, only comes 

 to the point at which we must needs arrive under a consider- 

 ation of the " web of relation" traceable in the constituents of 

 the solar system namely, that they have had a common 

 origin in a soft and diffused form of matter. Such a form of 

 matter may now, as is alleged, be no longer actually seen in 

 the heavens ; and yet there may remain good reasons for be- 

 lieving that it once existed. One of these will afterwards be 

 presented in the facts connected with the density of the planets 

 and the internal heat of the earth. Another rests in the 

 curious phenomenon called the Zodiacal Light, an oblate lumi- 

 nosity surrounding the sun, and very conspicuous in the twi- 

 lights of tropical climes ; a remnant, as has been supposed, of 

 the diffused solar atmosphere of the nebular cosmogony. There 

 is even a support to the theory in what would seem at first to 

 be an anomaly and an objection the existence of the many 

 binary and ternary solar systems. It may be supposed that, 

 at a certain point in the confluence of the matter of these 

 regions of space, the solar nuclei would become involved in a 

 common revolutionary motion, linked inextricably with each 

 other, though it might be at sufficient distances to allow of 

 each body having afterwards its attendant planets. Such a 

 phenomenon is occasionally realized to us on the surface of a 



