Page:Popular Science Monthly Volume 10.djvu/728

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fer a very considerable retardation in their passage through space. Encke's comet formerly came regularly back into the field of the earth's orbit once in every three years, but with a period shortened six hours each time. The whole planetary regions seem to be filled with collections of matter—star-dust and meteorites. They are all revolving about the sun in eccentric orbits, and are doubtless slowly circling toward it. The zodiacal light is supposed to be only an immense aggregation of this material. Thus the thickening stratum as these strange bodies draw near to the sun shows that they are all slowly gathering to that great centre of attraction.

The evident effect of the fall of any of the planets into the sun would be the diffusion of highly-heated vapors far out into the spaces that surround it—probably far enough to reach the next outlying planet, and thereby to increase its retardation and hasten its fall into the mighty caldron. So one by one the planets dissolve and their elements fill the void of space. The expanding gases catch up the waves of radiant heat that have long been wandering from planets and suns; and the nebula is again seething and surging with its mighty contending forces. Sun-system reaches out to sun-system, and star-galaxy mingles with star-galaxy, till through all the abysmal depths matter is again "without form and void, and darkness is upon the face of the deep." Chaos has returned once more, again to be breathed upon by the Omnipotent Spirit that reforms and recreates.


By Professor GEIKIE, F. R. S.,


FIELD-GEOLOGY does not mean and need not include the collecting of specimens. Consequently a formidable series of hammers and chisels, a capacious wallet with stores of wrapping-paper and pill-boxes, are not absolutely and always required. Rock-specimens and fossils are best collected after the field-geologist has made some progress with his examination of a district. He can then begin to see what rocks really deserve to be illustrated by specimens, and in what strata the search for fossils may be most advantageously conducted. He may have to do the collecting himself, or he may be able to employ a trained assistant, and direct him to the localities whence specimens are to be taken. But, in the first instance, his own efforts must be directed to the investigation of the geological structure of the region. The specimens required for his purpose in the early stages of his work do not involve much trouble. He can detach them and carry them off as he goes, while he leaves the full collection to be made afterward.