in size, and their average distance apart may perhaps be ten times as great. We will suppose that each galaxy is at the center of an otherwise unoccupied cube 10 andromedes on an edge. The radius of a sphere containing 450,000 such cubes is 760,000 light-years. Now Perrine estimates that there are at least 500,000 nebulæ in the heavens within reach by the Crossley reflector, and probably nine tenths of these are white nebulæ or galaxies. It is therefore safe to say that the light of the stars can travel for one million years before becoming so much reduced by intergalactic absorption as to be beyond the grasp of this powerful instrument.
The view which I now wish to present is that it is the ether itself which absorbs the radiation from the stars.
Considered merely as to its volume, the ether is so overwhelmingly immense that all other bodies shrink into nothingness in comparison. The radius of the sun is
ro = 7 X (10)5 kilometers.
Half the distance to the nearest star is
r* = 2 X (10)13 kilometers.
An ethereal sphere which may be called the sun's own, being bounded by the similar spheres of neighboring stars, may be drawn with the latter radius. The radius of the sun bears to that of its interstellar sphere the ratio
ro : r* = 1 : 30,000,000,
and the volume of the associated ether exceeds that occupied by the solar substance in the ratio
(r)3 : (ro)3 = 2.7 X (10)22 : 1.
Since there are vacant spaces between neighboring galaxies, something must be allowed for these. Let us suppose that the ethereal volume is four hundred times greater than that just given, or that its volume ratio is
Ether volume : Matter volume = (10)24 : 1.
This allows a considerable extension of thinly scattered stars around each galaxy, and places the galaxies at relatively smaller distances from each other than the stars, if distances are expressed in terms of diameters, an arrangement which is indicated by the evidence already presented.
The next step in the argument demands an estimate of the total light from all of the stars. Call this L. Newcomb gave us such a photometric measurement, and found
L = 600 stars of zero magnitude.
The brightness of the sun is