Page:The American Cyclopædia (1879) Volume VII.djvu/572

 560 GALAXY GALBA a minute vertical angle, and the sun placed exactly at the vertex, while the remotest por- tion of the space thus occupied with stars is at least twenty-seven times further away than the nearest ? Such a portion of space would have the shape of a long straight rod very delicate in its proportions. Apart from the antecedent improbability of such an arrangement, it is certain that a cluster of stars so shaped would have no dynamical stability. Moreover, the cluster in Perseus is not a solitary instance, since upward of thirty similar clusterings were counted by Herschel in the northern heavens alone, and Sir John Herschel observed many more in the southern portions of the milky way. These considerations seem to dispose of the principle on which Sir W. Herschel based this his latest method of star gauging. It seems demonstrated by the evidence that the stars seen in the clustering aggregations of the milky way are of many orders of real magnitude, and arranged at distances among which there is not even an approach to general uniformity. Sir John Herschel's observations of the milky way in the southern heavens go far to confirm these conclusions, though he himself adopted a theory in some sense re- sembling that which his father advanced in 1785 ; only that instead of regarding the galaxy as shaped like a cloven disk, he held that it resembles in figure a flat ring (cloven, neces- sarily, to explain the double portion of the milky way). The elder Struve was among the first to point out that the arrangement of the brighter stars over the heavens does not accord with either the cloven disk or the cloven ring theory of the galaxy. He found that the stars down to the eighth magnitude, which according to either theory should show no marked gathering toward the milky way zone, are nevertheless aggregated in the most striking manner upon that region. Hence Struve inferred that there is an aggregation of stars toward the medial plane of the milky way ; and he adopted (quite unnecessarily, as it appears to the present writer) the theory that the range of stars constituting the milky way stratum is illimitable in all directions lying within that stratum. Struve's theory of an indefinite extension of the milky way in its own plane seems disposed of by the younger Herschel's observation that "throughout by far the largest portion of the extent of the milky way in both hemispheres, the general blackness of the ground of the heavens on which its stars are projected, and the absence of that innumerable multitude and excessive crowding of the smallest visible magnitudes,, too small to affect the eye singly, which the contrary supposition would appear to necessi- tate, must, we think, be considered unequivo- cal indications that its dimensions, in direc- tions where these conditions obtain, are not only not infinite, but that the space-penetrating power of our telescopes suffices fairly to pierce through and beyond it." Moreover, Sir John Herschel disposed very completely of the rea- soning on which Struve based the theory that light is gradually extinguished in its passage through space. " We are not at liberty," he said, u tp argue that at one part of the milky way's circumference our view is limited by this sort of cosmical veil which extinguishes the smaller magnitudes, cuts off the nebulous light of distant masses, and closes our view in impenetrable darkness; while at another we are compelled, by the clearest evidence our telescopes can afford, to believe that star- strewn vistas lie open, exhausting their pow- ers and stretching beyond their utmost reach 7 as is proved by that very phenomenon which the existence of such a veil would render impossible, viz., infinite increase of number and diminution of magnitude, terminating in complete irresolvable nebulosity." Recent re- ' searches have led to the inference that the structure of the galaxy is not so simple as any of the theories advanced by the Herschels or Struve would imply. The stars, even in one and the same portion of the galaxy, seem to present all those varieties of size and aggre- gation which have hitherto been ascribed to the effects of distance. It appears that often where the Herschels supposed that they were passing further and further, by means of their powerful telescopes, into the depths of space, they were in reality merely searching more and more scrutinizingly a particular region of our star system. The galaxy, according to these more modern views, would come to be re- garded as an infinitely complicated spiral, with outlying branches extending beyond the range of the most powerful telescopes yet made. Moreover, it seems as if those mysterious ob- jects the nebulae, instead of being distant gal- axies as had been supposed (at least as respects the stellar nebulse), were in reality but portions of our own sidereal system. It is at least cer- tain that the mysteries of the galaxy have not yet been fully solved, even if any noteworthy advance has been made toward their solution. GALBA, Serving Snlpicins, a Roman emperor, born near Terracina, Dec. 24, 3 B. C., died Jan. 15, A. D. 69. As he inherited great wealth and possessed great talents, it was predicted both by Augustus and Tiberius that he would become the head of the Roman world. He attained the prsetorship in A. D. 20, and the consulship in 33, carried on a war in Gaul in 39 against the Germans, was intrusted with the administration of Africa in 45, lived in retire- ment for several years under Nero, but in 61 was invested with the government of Hispania Tarraconensis. He was faithful to the emperor till in 68 Vindex rebelled in Gaul, and his own assassination was plotted by Nero. He then took the title of legate of the Roman senate and people, marched toward Rome, and on the death of Nero received the imperial dignity from the senate. He offended the praetorian guard by refusing the donative which bad been promised in his name, and completed his ruin