534 THE POPULAR SCIENCE MONTHLY 



the lighted rim toward the center. They are the beginnings of those 

 spoke-like markings the methodical oddity of which makes their actu- 

 ality so difficult of belief. They seem a thought too peripherally posi- 

 tioned to be other than optically evolved. Their recurrent showing in 

 the same places marks them as facts, however, and as such we must 

 regard them. Now when we consider them in the light of Venus's 

 meteorology their cause at once suggests itself. And with this index- 

 finger to guide us we perceive that far from being surprising they are 

 just the phenomena we ought to expect. For consider the surface 

 indraught along the bounding rim of constant sun-exposure. With the 

 immense temperature gradient which exists between the day and the 

 night side of Venus, the power of these winds must be enormous. Being 

 essentially surface ones, they must sweep the face of the planet with 

 irresistible force and, what is more, having once found a pathway of 

 preference, must from the general unchangeableness of the conditions 

 continue to follow it perpetually. For the only thing to alter their 

 direction, the libration, is from the circularity of Venus's orbit negli- 

 gibly small. Sweeping in originally through valleys or mountain passes, 

 the points offering the easiest access, they must eventually have polished 

 the surfaces over which they passed to a differentiation of appearance 

 visible even across millions of miles of intervening space. Essentially 

 surface currents at the rim, they would become less and less so as they 

 neared the center of the lighted side and furthermore would converge 

 as they approached it. They would seem to us to narrow and become 

 at the same time less salient as they advanced. This is just what their 

 spoke-like character shows. Thus the peculiar look of the Venusian 

 markings proves to be in exact keeping with what the conditions de- 

 mand, and by so doing bears testimony that those conditions actually 

 exist. 



Not less strange on its face and equally interesting for its disclosure 

 is another phenomenon connected with the planet which also has been 

 deemed incredible — the exceeding brightness of Venus's disk. Her 

 great luster is, as we saw above, in part attributable to her proximity 

 first to the sun and secondly to us. But this is not the sole cause of it. 

 Though a part of her splendor is due to her position, a part is her own. 

 Her intrinsic brightness, her albedo, as it is called, has been found by 

 Miiller, of Potsdam, who has made the last and most authoritative 

 determination of it, to reach the excessive figure of .92 of absolute 

 reflection. This figure has seemed to many impossible, but we shall 

 see from consideration that it simply reflects the conditions. 



The rising currents on the sunward side must from their great heat 

 be capable of holding much water-vapor in suspension. This they 

 would take over with them in large part to the night side and becoming 

 chilled there deposit it as snow. Being cold on their return they would 

 reenter the warm side relatively dry and thus be fitted to act again as 

 water-carriers from that side to the other. This process of depletion 



