322 ANNUAL OF SCIENTIFIC DISCOVEKY. 



within our reach, we mav be led to some interesting conclusions. We 



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shall, of course, suppose the case of the nearest approach of either of 

 those planets when they pass between ourselves and the sun. In such 

 circumstances, an apparently retrograde motion will bring us up with 

 a great broad disc into their midnight sky, and all our features will lie 

 open before the distant observer's gaze. There can be little question 

 that the distinction of our continents and oceans would be very per- 

 ceptible from the superior reflective power of the former as con- 

 trasted with the absorbent property of the latter, which, as is shown 

 by experiments with the diving-bell, soon extinguishes the solar rays. 

 The general aspect of the land would, no doubt, be various from the 

 effect of local color where sufficiently extensive, and the vegetation 

 of the prairies and pampas would be readily distinguishable from the 

 sands of the Sahara ; but diversities on a smaller scale would be 

 merged by distance in a compound gray of the third order of color. 

 The appearance of the water would also be greatly contrasted in 

 different parts, from its varying degrees of depth and consequent 

 translucency. Islands would, of course, be in general perceptible in 

 proportion to their size as brighter specks ; but it may admit of a 

 question whether an island, or, indeed, a line of coast, would be in all 

 cases easily distinguished from an adjacent shallow sea. The polar 

 regions of ice and snow would, of course, be strongly marked, with 

 their extension or contraction according to the time of year ; but, in 

 consequence of the inclination of the earth's axis, their presentation 

 would differ greatly at different seasons. If the supposed opposition 

 of the earth should coincide with our European summer, the north 

 snows would alone be conspicuous, entering far into the visible hem- 

 isphere, but diminishing gradually with the continued action of the 

 sun ; if during our winter, the reverse would occur ; in spring or 

 autumn each pole would show its white segment at the edge of the 

 disc ; but in every case, as our poles of temperature are not coinci- 

 dent with our poles of rotation, and our continental are very different 

 from our insular climates, the brightness of our arctic and antarctic 

 regions would be unsynimetrical in extent, and their aspect would 

 differ materially as different sides of our globe were brought round 

 by our diurnal rotation. The frozen summits of such extensive ranges 

 as the Himalaya or Andes would, no doubt, be perceptible with suffi- 

 cient optical power; but the shadows of our mountains would, of 

 course, be equally invisible with those in the full moon, and from the 

 same cause ; and it does not seem likely that even our largest river- 

 courses would have sufficient magnitude to be seen. As the rotation 

 of our globe, combined with the inclination of its axis, would, in suc- 

 cessive oppositions, bring the whole of the surface before the eye, it 

 might at first be thought an easy task to map all its outlines with 

 precision ; but the atmosphere would in all likelihood interpose most 

 serious difficulties. From its property of transmitting red light, as 

 shown in our sunrise and sunset, and in the face of the totally eclipsed 

 moon, it will probably communicate a slight ruddy tinge to our disc, 

 like a faint wash of red passed over a drawing ; but this hue would 

 be very feeble, if at all apparent, in the centre, coming out chiefly 

 from the oblique transit of the ray through the atmosphere towards 

 the edges of the globe ; and it would be immaterial compared with 



