Page:Popular Science Monthly Volume 8.djvu/289

Rh copied; and although only an occasional and unfrequent reference could be made to a lamp, the stars within it had become so familiar by their constant recurrence, that the memory could as easily as before retain its estimates of distance and direction, until mutual comparison could be made between the map and the heavens."

It will be seen what a great advance had been made in the conception of the application of the topographical method of contour lines to the delineation of degrees of brightness, although this method has practical limitations not spoken of by Mason, and we must consider the careful separation of the various results into classes ranged according to their degrees of certainty, as scarcely less important. In all former memoirs the chart included all the results reached, and there was no searching division of these in such a way as to give absolute data to the future investigator.

Throughout the entire memoir (which relates also to other nebulae than the one now in question) the whole endeavor is to reach a perfect definiteness of conception; and Mason evidently held the idea that, in the existing state of astronomy, it was eminently "better to do one thing well than many things indifferently."



Lamont tells us in Annalen der K. Sternwarte bei München, Band xvii. (1868), that his early researches on this and other nebulæ were prosecuted in the hope that something might be determined as to their