128 SCHIAPARELLI'S LATEST VIEWS RAGARDING MARS. 



rendered visible at the distance of Mars— by a variety of coloring. A 

 similar system of operations produced in that planet may tlius certainly 

 be rendered visible to ns. But liow difBcult for tlie Lunarians and tlie 

 Areaus to be able to imagine tbe true causes of such changes of appear- 

 ance without having first at least some superficial knowledge of terres- 

 trial nature! So also for us, who know so little of the physical state 

 of Mars, and nothing of its organic world, the great liberty of possible 

 supposition renders arbitrary all explanations of this sort and consti- 

 tutes the gravest obstacle to the acquisition of well-founded notions. 

 All that we may hope is that with time the uncertainty of the problem 

 will gradually diminish, demonstrating if not what the geminations 

 are, at least what they can not be. We may also confide a little in 

 what Galileo called "the courtesy of nature," thanks to which a ray 

 of light from an unexpected source will sometimes illuminate an inves- 

 tigation at first believed inaccessible to our speculations, and of which 

 we have a beautiful example in celestial chemistry. Let us therefore 

 hope and study. 



