Alfred Russel Wallace 



left much alone at this period, he began to vary his pur- 

 suits by studying a book on Nautical Astronomy, and 

 constructing a rude telescope.' This primitive appliance 

 increased his interest in other astronomical instruments, 

 and especially in the grand onward march of astronomical 

 discovery, which he looked upon as one of the wonders of 

 the nineteenth century. 



It was the inclusion of astronomy in lectures he delivered 

 at Davos which led him to extend his original brief notes 

 into the four chapters which form an important part of his 

 " Wonderful Century." He freely confessed that in order 

 to write these chapters he was obliged to read widely, and 

 to make much use of friends to whom astronomy was a 

 more familiar study. And it was whilst he was engaged 

 upon these chapters that his attention became riveted upon 

 the unique position of our planet in relation to the solar 

 system. 



He had noticed that certain definite conditions appeared to 

 be absolutely essential to the origin and development of the 

 higher types of terrestrial life, and that most of these must 

 have been certainly dependent on a very delicate balance of 

 the forces concerned in the evolution of our planet. Our 

 position in the solar system appeared to him to be peculiar 

 and unique because, he thought, we may be almost sure 

 that these conditions do not coexist on any other planet, 

 and that we have no good reason to believe that other 

 planets could have maintained over a period of millions of 

 years the complex and equable conditions absolutely neces- 

 sary to the existence of the higher forms of terrestrial life. 

 Therefore it appeared to him to be proved that our earth 

 does really stand alone in the solar system by reason of 

 its special adaptation for the development of human life. 



Granting this, however, the question might still be asked, 



J See Vol. I., p. 20. 



i68 



