Page:The American Cyclopædia (1879) Volume XV.djvu/328

 316 STAR Astrononische Nachrichten, vol. xxvi., No. 622 (published in 1848), maintaining the same view of the invalidity of M. Struve's reasoning, and questioning the hypotheses (of which M. Encke reckons five) tacitly assumed by him." The present writer, led independently to the same general views respecting Herschel's labors which Struve had formed, and afterward to the same general views respecting Struve's la- bore which Forbes and Encke formed, adopted the following as the principle on which fresh researches should be based: That as regards the laws of stellar distribution, the range of stellar magnitude, intrinsic brilliancy, and so on, we must assume nothing, all assumptions having been proved by the clearest possible evidence to be untrustworthy. We must be guided by the facts alone. Nor are we thus compelled to abandon ai hopeless the great problem of the star depths. Even where Her- schel's methods seemed to fail, they afford ex- cellent promise of success. His first method, for example, had to be abandoned, so far as his original purpose was concerned, because he found reason to believe that the great rich regions of the milky way are situated like mighty clouds of stars in space, and are not mere ranges of stars extending continuously from our own neighborhood. But it was the method itself which taught this, which in fact effected this capital discovery. The second method, again, cannot be interpreted as Her- schel hoped ; it cannot tell us how far off, rel- atively, are different star groups. But this application of the method has to be abandoned simply because the use of the method itself has taught us that the architecture of the heavens is far too complex to be interpreted in so sim- ple a manner. Here then is another great dis- covery effected by a method of star gauging which, so far as its original purpose was con- cerned, has had to be rejected. But so soon as we recognize these facts, a method of re- search is suggested which combines the trust- worthy qualities of both methods, and is free from the faults of either. We must employ Herschel's first method of star gauging, count- ing the stars in equal fields with the same tele- scope ; but we must not limit ourselves to the study of a star field here and there. The whole heavens must be surveyed, and this not with one telescopic power only, but with many, from the lowest powers to the highest avail- able. The results obtained with each power must be compared together, after being care- fully indicated in suitable charts; a method altogether more satisfactory than any pro- cesses of statistical enumeration. Differential charts, showing by how much each increase of power increases in each region the number of stars brought into view, ought also to be con- structed. No preconceived opinions should be suffered to mar the teachings thus obtained ; but the architecture of the heavens must be viewed precisely as it is presented to us by these results. Principles of interpretation, however, may legitimately be applied to the evidence, so long as they are founded on just considerations. It appears to the writer that the following principles are not open to ques- tion in this respect: 1. Where two surveys made with different telescopic powers indicate concordant laws of distribution over the heav- ens, the rich regions thus indicated are regions where the orders of objects dealt with by the two telescopes are intermingled. 2. Where .instead of such accordance a law of contrast is indicated, regions rich in one order of ob- jects being poor in another and vice versa, the two orders still belong to one system, but some peculiarity in the laws according to which they were formed causes them to occupy different parts of the system, segregating as it were from each other. 3. Where no connection whatever either of agreement or contrast can be recognized, it is probable, and in general presumable, that the two orders are altogether distinct and lie at different distances from each other. 4. Where partial or local agreement or contrast is indicated, the inference is that the true arrangement of the objects in space is affected both by laws of aggregation or segre- gation and by diversities of distance, and by one cause or the other to a degree correspond- ing to the extent of such agreement or con- trast. What is here said of objects brought into view by different telescopic powers is true of different orders of objects, as nebulae, dou- ble stars, colored stars, variables, and so on. These principles have been applied by the writer already to stars visible to the naked eye in both hemispheres, to stars down to the tenth magnitude of Argelander in the northern hemisphere only, and to the known nebulaa (5,500 in number) in both hemispheres. As an illustration of the fertility of the process, the following results may be indicated : First, the stars visible to the naked eye are not dis- tributed uniformly through surrounding space, but are gathered markedly in two rich regions, one northern, the other (larger) southern, and are particularly rich in the region of the milky way; but the leading orders of these stars are gathered zonewise in a region some- what inclined to the milky way; a circum- stance first noted by Sir J. Herschel, but inde- pendently by the present writer and also by Prof. B. A. Gould. The northern stars, down to the tenth magnitude inclusive, are gathered in the most marked manner in the galactic zone, not increasing gradually in richness of distribution as they approach it, but being gathered richly in the nodules, clustering ag- gregations, streams, and whorls of stars of which the galaxy consists. This circumstance proves that the milky way is not only appar- ently but really so formed; and since Her- schel's gauges show that wherever the milky way appears bright to the naked eye, there the fainter orders of stars, down to the least lirought into view by his great telescope, are most richly strewn, it follows that these fainter