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TEE POPULAR SCIENCE MONTELY.— SUPPLEMENT. 



that it would have to be estimated rather than 

 actually seen, yet there would be no difficulty in 

 thus perceiving it with the mind's eye. The rate 

 of motion, indeed, would almost be exactly the 

 same as that of the equatorial part of the surface 

 of Mars, in consequence of the planet's rotation ; 

 and this (as is well known to telescopists), though 

 not discernible, directly produces, even in a few 

 minutes, changes which a good eye can clearly 

 recognize. We can scarcely doubt, then, that if 

 our earth were so situated at any time when one 

 of the great waves generated by Peruvian earth- 

 quakes is traversing the Pacific that the hemi- 

 sphere containing this ocean were turned fully 

 illuminated toward Venus (favorably placed for 

 observing her), the disturbance of the Pacific 

 could be observed and measured by telescopists 

 on that planet. 



Unfortunately, there is little chance that ter- 

 restrial observers will ever be able to watch the 

 progress of great waves athwart the oceans of 

 Mars, and still less that any disturbance of the 

 frame of Venus should become discernible to us 

 by its effects. We can scarcely even be assured 

 that there are lands and seas on Venus, so far as 

 direct observation is concerned, so unfavorably is 

 she always placed for observation ; and though 

 we see Mars under much more favorable condi- 

 tions, his seas are too small and would seem to 

 be too shallow (compared with our own) for great 

 waves to traverse them such as could be dis- 

 cerned from the earth. 



Yet it may be well to remember the possibil- 

 ity that changes may at times take place in the 

 nearer planets — thet errestrial planets, as they are 

 commonly called, Mars, Venus, and Mercury — 

 such as telescopic observation under favorable 

 conditions might detect. Telescopists have, in- 

 deed, described apparent changes, lasting only for 

 a short time, in the appearance of one of these 

 planets, Mars, which may fairly be attributed to 

 disturbances affecting its surface in no greater 

 degree than the great Peruvian earthquakes have 

 affected for a time the surface of our earth. For 



instance, the American astronomer Mitchel says 

 that, on the night of July 12, 1845, the bright po- 

 lar snows of Mars exhibited an appearance never 

 noticed at any preceding or succeeding observa- 

 tion. In the very centre of the white surface ap- 

 peared a dark spot, which retained its position . 

 during several hours. On the following evening 

 not a trace of the spot could be seen. Again, 

 the same observer says that, on the evening of 

 August 30, 1845, he observed for the first time a 

 small bright spot, nearly or quite round, project- 

 ing out of the lower side of the polar spot. " In 

 the early part of the evening," he says, "the 

 small bright spot seemed to be partly buried in 

 the large one. After the lapse of an hour or more 

 my attention was again directed to the planet, 

 when I was astonished to find a manifest change 

 in the position of the small bright spot. It had 

 apparently separated from the large spot, and 

 the edges alone of the two were now in contact, 

 whereas when first seen they overlapped by an 

 amount quite equal to one-third of the diameter 

 of the small one. This, however, was merely an 

 optical phenomenon, for on the next evening the 

 spots went through the same apparent changes, 

 as the planet went through the corresponding 

 part of its rotation. But it showed the spots to 

 be real ice-masses. The strange part of the story 

 is, that in the course of a few days the smaller 

 spot, which must have been a mass of snow and 

 ice as large as Nova Zembla, gradually disap- 

 peared." Probably some great shock had sepa- 

 rated an enormous field of ice from the polar 

 snows, and it had eventually been broken up and 

 its fragments carried away from the arctic regions 

 by currents in the Martian oceans. It appears 

 to us that the study of our own earth, and of the 

 changes and occasional convulsions which affect 

 its surface, gives to the observation of such phe- 

 nomena as we have just described a new interest. 

 Or rather, perhaps, it is not too much to say that 

 telescopic observations of the planets derive their 

 only real interest from such considerations. — 

 Comhill Magazine. 



