Il6 THE BORDERLAND OF SCIENCE. 



each of two points nearly opposite to each other on the 

 globe of the planet, a white spot could be recognised, 

 whose light, indeed, was so brilliant as to far outshine 

 that emitted by the remainder of the disc. The idea 

 that these white spots correspond in any way to the 

 polar snows on our own earth does not seem to have 

 occurred to Maraldi. Yet he made observations which 

 were well calculated to suggest the idea, for he noticed 

 that one of the spots had at a certain time diminished 

 greatly in size. Instead, however, of ascribing this 

 change to the progress of the Martial seasons, he was 

 led to the strange conclusion that the white spot was 

 undergoing a process of continuous decrease, and he 

 even announced the date when, as he supposed, it would 

 finally disappear. 



No such disappearance took place, however. When 

 Sir W. Herschel began his series of observations upon 

 Mars, more than half a century later, the spots were 

 still there. The energy of our great astronomer did 

 not suffer these striking features to remain long un- 

 examined. Searching, as was his wont, after terrestrial 

 analogies or, at least, analogies depending on known 

 facts he was quickly led to associate the white spots 

 with our arctic regions. It would follow, of course, 

 that in the summer months of either Martial hemi- 

 sphere, the snow-cap would be reduced in size, while in 

 the winter it would attain its greatest dimensions. Sir 

 W. Herschel found this to be the case, and he was able 

 to show that the changes which Maraldi had inter- 

 preted as suggesting the eventual disappearance of one 



