resemblances to the Earth consisted mainly in the similar distri- 

 bution of land and sea, and the existence of polar caps which 

 changed with the seasons. The chief differences were (a) much 

 less heat obtainable from the sun owing to greater distance ; (b) 

 much longer time of revolution ; (c) force of gravity about two- 

 fifths of ours, thus affecting the density, pressure, and tempera- 

 ture of its atmosphere. The whole subject was very complex and 

 did not lend itself to treatment by Analogy. 



The Inductive methods, however, led mainly to the dis- 

 covery of empirical laws, for which causes could not be assigned ; 

 the highest generalizations required the application of Hypo- 

 thesis, and Nature must be anticipated. From the days of 

 Newton this had produced most important results, such as the 

 discovery of the Law of Gravitation and that of Conservation of 

 Energy. Hypothesis was especially powerful when used as a 

 part of what Mr. Mill calls the Deductive method, which consisted 

 of three steps : — 



( 1 ) A fact was established provisionally by direct Induction . 



(2) A Hypothesis was formed which reasonably explained 



the fact. 



(3) Severe appeals to observation or experiment in test 



cases finally determined the fate of the Hypothesis. 

 Such were in brief outline the forms of reasoning specially 

 used, whether consciously or unconsciously in scientific research, 

 and their study and application were valuable to those who wished 

 to avoid mistakes. Failures would, however, occur as in the past. 

 Throughout all an unbiassed attitude must be maintained, such 

 as Michael Faraday expressed in the following words : — " The 

 world little knows how many of tbe thoughts and theories which 

 have passed through the mind of a scientific investigator have 

 been crushed in silence and secrecy by his own severe criticism 

 and adverse examination ; that in the most successful instances 

 not a tenth of the suggestions, the hopes, the wishes, the pre- 

 liminary conclusions have been realized." 



