510 Mr. D. Vaughan on Phenomena which may be traced 
309 or 318 years. Under the most favourable circumstances 
for manifesting such an extraordinary inequality between its 
periods of light and darkness, the surface of the supposed 
distant sphere must be nearly 200,000,000 times as great as 
the part of it sending light to our planet during the period of 
maximum brightness. The light, moreover, must have pro- 
ceeded from the verge of the invisible disk; and this circum- 
stance, taken in connexion with the surprising brilliance of 
the star of 1572, together with the invariability of its position, 
will compel us to ascribe to the spectral orb in question a dia- 
meter far exceeding that of Neptune’s orbit. We must also 
regard these vast bodies as solid; for, if composed of liquid or 
gaseous matter, they could not have the luminosity confined to 
particular localities. Even if stellar movements could permit 
us to suppose the existence of such stupendous spheres, the 
explanation would be applicable to one or two cases only; and 
we must therefore reject a hypothesis whose claims rests solely 
on the greater imperfections of others proposed to account for 
the same phenomena. 
But investigations respecting the necessary course of physical 
events in the dark systems afford still more important evidence 
in regard to the ethereal contents of space. Were the central 
body composed of solid matter, or surrounded with an atmo- 
sphere of oxygen, nitrogen, or carbonic acid, a development of 
heat and light might be expected to attend the dilapidation of 
one of the satellites, or the ultimate incorporation of its matter 
with the great orb; but the appearance would not correspond 
to that exhibited by the temporary stars. Admutting that a 
solid globe, almost as large as the sun, may be rendered so 
highly meandescent as to shine like the star of 1572 in its 
greatest brilliancy, it would be impossible for it to cool so 
rapidly as to become invisible in the course of seventeen months. 
Besides this, it may be easily shown that, if our earth had a 
diameter of 80,000 miles, with its present density and superfi- 
cial temperature, our atmosphere would have its density reduced 
a millionfold with an elevation of six or seven miles. Thus, 
the greater mass we assign to the central body, the more nar- 
row must we regard the atmospheric region where light can be 
developed by aérial compression ; and the less display of lustre 
could we expect from this cause when a satellite fell from its 
stage of planetary existence. But this difficulty will disappear 
when we suppose that the ether of space forms for the several 
great celestial bodies extensive atmospheres, which are rendered 
luminous by adequate compression, or rather by the chemical 
action it induces—a theory which becomes necessary to account 
for the luminosity of meteors and the perpetual brilliancy of suns, 
