Page:Popular Science Monthly Volume 15.djvu/529

Rh of climate and of individual eye-sight affect this considerably. Argelander, and after him Heis, catalogued all the stars visible to their eyes; their numbers, for the whole northern hemisphere, where 2,350 and 3,936 respectively. Heis, must therefore, have seen stars at least four tenths of a magnitude fainter than Argelander's faintest. La Caille's eye must also have been sharper than the average; and, if Mr. Proctor had thought to apply the test of enumeration to the different magnitudes in different parts of the sky, this explanation would doubtless have occurred to him, and nothing have been heard of his remarkable "rich region." His observation is valuable, certainly; but only by showing the undeveloped state of the whole subject, and the precautions necessary before venturing conclusions on it.

The search for a common center, about which the uncounted millions of stars composing the galactic cluster may revolve, has tempted many investigators, but it can not be said as yet to have proved altogether successful. Mädler, by calculations from the proper motions of stars in different parts of the heavens, sought to locate it among the Pleiades; some later astronomers have preferred the Sword of Perseus; Mr. Maxwell Hall has just decided, and informed the Astronomical Society of England, that the universe turns about the South Elbow of Andromeda. The proof advanced is always incomplete, resting on assumptions not generally admitted; and when we remember that the gravitative force exerted by the fixed stars on one another is so small that to keep the nearest of them from falling to the sun, supposing no counterbalancing attractions, an angular velocity of but one second of arc in eighty years is needed; that the proper motions to be explained are often far larger than this; that the distance of the attracting center must be many times that of the nearest fixed star; and that the heavens give no sign of any preeminent body or group of bodies to which we may ascribe the enormous attractive power necessary to control these motions—the skepticism of many astronomers as to the universal center seems excusable.

It must be admitted, then, that but little of the true character of our sidereal system is known to us, and that all speculation upon it rests as yet on a very insecure foundation. But, as the sudden development of spectrum analysis has shown, matters of pure conjecture to-day may become entirely settled to-morrow; and it may reasonably be hoped that the secrets of this domain, if due interest be taken in them, will not much longer elude the search of scientific explorers.