Masterpieces of Science 



which prevail throughout the universe of matter. 



The progress of our knowledge as to the plan- 

 ets themselves and what we may call their per- 

 sonal peculiarities will probably depend largely 

 upon the improvement of our means and meth- 

 ods of observation. The grotesque discrepan- 

 cies and contradictions between the reported 

 results of different observers now throws more 

 or less doubt on the conclusions of all. And yet 

 the unquestionable gains that have accrued within 

 the last twenty years are very encouraging. It 

 seems to be fairly proved that the two inner 

 planets imitate the behaviour of the moon in 

 keeping always the same face towards the sun, 

 and the observations of the elder Herschel and 

 others, which indicate a similar peculiarity in 

 some of the satellites of Jupiter and Saturn, have 

 lately received direct confirmation. We may 

 now, therefore, with reasonable confidence, as- 

 sume the theory of "tidal evolution" as a guid- 

 ing clue in our study of the development of the 

 planetary system. 



As to the nature and interpretation of the 

 markings seen upon the surface of the different 

 planets, much uncertainty still remains, which 

 time may be expected to remove. If we could 

 reasonably adopt the reports and descriptions 

 of some single one of the observers who have 

 devoted themselves to the study, we might 

 logically reach pretty definite conclusions. But 

 until the agreement between observers is im- 

 proved we can only hesitate and wait for more 

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