378 The Earth in Opposition. 



from, our insular climates,* the brightness of our arctic r and 

 antarctic regions would be unsymnietrical in extent, and their 

 aspect would differ materially as different sides of our globe 

 were brought round by our diurnal rotation. The frozen sum- 

 mits of such extensive ranges as the Himalaya or Andes would 

 no doubt be perceptible with sufficient 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 

 successive 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 like- 

 lihood 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 com- 

 municate 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 the confusion arising from the local condensation of its 

 watery particles. There can be no doubt that Schroter was 

 mistaken in thinking that accumulations of vapour would appear 

 as dark spots upon a planetary disc ; the worthy old Hanoverian 

 (and a very worthy fellow he seems to have been) confounded 

 the interior effect, or that produced upon an eye beneath them, 

 which, of course, would be one of gloom from intercepted 

 light, with the exterior aspect to a distant observer, which 

 would be eminently luminous, few bodies reflecting a more 

 intense white light than the upper surface of a densely com- 

 pacted cloud : and hence those regions of the earth which are 

 sometimes for months together overshadowed by a cloudy pall, 

 niust, to an external eye, present a peculiarly white and lumi- 

 nous appearance ; while, for a like reason, the edges of the disc, 

 where oblique vision would render vapour more perceptible, 

 would possess not only the ruddier, as before suggested, but 

 the more vivid light. And thus it is easy to see how baffling an 

 impediment our atmospheric variations must interpose in the 

 way of any accurate comprehension and delineation of the 

 features of our globe, and how the configurations which a 

 distant observer would at one time congratulate himself upon 

 having satisfactorily traced, might, after a short interval, be 

 wholly defaced and obliterated, or so intermingled with the 



* See tins fact admirably illustrated by Professor C. Piozzi Smyth, in Ins 

 most interesting and pleasant book, Three Cities in Russia. 



