But it has been well said that the structure of the universe "has a fascination of its own for most readers quite apart from any real progress which may be made towards its solution."[467] The Milky Way itself, Mr. Stratonoff considers to be an agglomeration of immense condensations, or stellar clouds, which are scattered round the region of the galactic equator. These clouds, or masses of stars, sometimes leave spaces between them, and sometimes they overlap, and in this way he accounts for the great rifts, like the Coal Sack, which allow us to see through this great circle of light. He finds other condensations of stars; the nearest is one of which our sun is a member, chiefly composed of stars of the higher magnitudes which "thin out rapidly as the Milky Way is approached." There are other condensations: one in stars of magnitudes 6·5 to 8·5; and a third, farther off, in stars of magnitudes 7·6 to 8. These may be called opera-glass, or field-glass stars. Stratonoff finds that stars with spectra of the first type (class A, B, C, and D of Harvard) which include the Sirian and Orion stars, are principally situated near the Milky Way, while those of type II. (which includes the solar stars) "are principally condensed in a region coinciding roughly with the terrestrial pole, and only show a slight increase, as compared with other stars, as the galaxy is approached."[468] Prof. Kapteyn thinks that "undoubtedly one of the greatest difficulties, if not the greatest of all, in the way of obtaining an understanding of the real distribution of the stars in space, lies in our uncertainty about the amount of loss suffered by the light of the stars on its way to the observer."[469] He says, "There can be little doubt in my opinion, about the existence of absorption in space, and I think that even a good guess as to the order of its amount can be made. For, first we know that space contains an enormous mass of meteoric matter. This matter must necessarily intercept some part of the star-light." This absorption, however, seems to be comparatively small. Kapteyn finds a value of 0·016 (about 1/60th) of a magnitude for a star at a distance corresponding to a parallax of one-tenth of a second (about 33 "light years"). This is a quantity almost imperceptible in the most delicate photometer. But for very great distances--such as 3000 "light years"--the absorption would evidently become very considerable, and would account satisfactorily for the gradual "thinning out" of the fainter stars. If this were fully proved, we should have to consider the fainter stars of the Milky Way to be in all probability fairly large suns, the light of which is reduced by absorption. That some of the ancients knew that the Milky Way is composed of stars is shown by the following lines translated from Ovid:--