Page:The fairy tales of science.djvu/227

 Herschel have catalogued above 4000! What an inexhaustible field of speculation and conjecture is opened here to the imagination! The finite mind of man, with its limited comprehensive powers, is bewildered and lost in the interminable range of system upon system, firmament upon firmament, of stars, each of them a sun, and probably in its sphere the presiding centre round which planetary worlds may be revolving, the dwelling-places, perchance, of intelligences of an immeasurably superior order to ours.

The classification of stars into magnitudes by estimation of their relative brightness, although unquestionably much more rational than the unmeaning division into constellations, is, however, entirely arbitrary. As we can only judge of the brightness of a star by the total impression made by its light upon the eye, it is quite evident that the assumed magnitude will depend, first, on its distance from us; second, on the absolute extent of its illuminated surface; third, on the intrinsic brightness of that surface;—and of these data we know nothing, or next to nothing. Up to a recent period we only knew that the nearest fixed stars could not possibly be