MARS AS A WORLD. 153 



invisible, and then to reappear, it has been possible to 

 discover the period of his rotation with much accuracy. 

 This period is singularly close to that of our earth ; there 

 is not three-quarters of an hour's difference, the duration 

 of the rotation of Mars being the greater, or stated exactly, 

 24 hrs. 37 min. 23 sec. 



It is, however, the telescopic aspect of the planet itself 

 which is especially interesting. With the single excep- 

 tion of the moon, there is no other body in the universe 

 that our telescopes can investigate so closely as they can 

 the planet Mars. It is now more than two hundred and 

 fifty years since it began to receive that assiduous atten- 

 tion from astronomers which has been continued to the 

 present hour. Among the earliest observations we have 

 are those of Fontana, at Naples. His feeble telescope was 

 sufficient to show that on the ruddy face of the planet were 

 certain more or less definite markings. 



The nature of these marks on the globe has been now 

 so carefully studied that there can be no doubt that the 

 chief of them indicate permanent features on the planet. 

 In fact, astronomers have prepared several charts or actual 

 maps of the continents and oceans, or rather of the dark 

 regions which are presumably oceanic, and of the more 

 ruddy or often orange-coloured portions which seem to be 

 land. 



The entire surface of the planet is in some degree known 

 to us ; in this respect there is a notable difference between 

 Mars and the moon. Of the moon we are only acquainted 

 with that face of it which is turned towards the earth, 

 and the other side is eternally secluded. But as Mars 

 rotates, we see now one side of it and now another, and 



