By the collation and comparison of these, important inductions are obtainable. Thus Professor A. S. Herschel concludes that the earth passed through seven strata of meteoric bodies, having each a thickness of about 50,000 miles—in all about 350,000 miles. As the diameter of the visible nebulosity of Biela’s comet was but 40,000 miles when nearest the earth in 1832, the great thickness of these strata indicates something beyond the comet itself. Besides this, Mr. Hind’s calculation for the return of the primary comet shows that on November 27th it was 250 millions of miles from the earth. Those, however, who are determined to enjoy the sensation of supposing that they really have been brushed by the tail of a comet, still have the secondary comet to fall back upon. This, as already described, was broken off the original, from which it was seen gradually to diverge, but was still linked to it by an arch of nebulous matter. If this divergence has continued, it must now be far distant—sufficiently far to afford me an opportunity of safely adding another to the numerous speculations, viz., that we may, on November 27th, have plunged obliquely through this connecting arm of nebulous matter, which was seen stretching between the parent comet and its offshoot. The actual position of the meteoric strata above referred to is quite consistent with the hypothesis. THE “GREAT ICE AGE” AND THE ORIGIN OF THE “TILL.” The growth of science is becoming so overwhelming that the old subdivisions of human knowledge are no longer sufficient for the purpose of dividing the labor of experts. It is scarcely possible now for any man to become a naturalist, a chemist, or a physicist in the full sense of either term; he must, if he aims at thoroughness, be satisfied with a general knowledge of the great body of science, and a special and a full acquaintance with only one or two of its minor subdivisions. Thus geology, though but a branch of natural history, and the youngest of its branches, has now become so extensive that its ablest votaries are compelled to devote their best efforts to the study of sections which but a few years ago were scarcely definable. Glaciation is one of these, which now demands its own elementary text-books over and above the monographs of original investigators. This demand has been well supplied by Mr. James Geikie in the “The Great Ice Age,”[15] of which a second edition has just been issued. Every student of glacial phenomena owes to Mr. Geikie a heavy debt of gratitude for the invaluable collection of facts and philosophy which this work presents. It may now be fairly described as a standard treatise on the subject which it treats.