TI PREFACE. 



essays as appear in that magazine may be regarded as the 

 selected work of the author to whom they are due. And 

 the fact that, after already drawing from this source, so 

 large a volume as the present can be formed from my 

 Cornhill essays, though seven or eight papers are for 

 various reasons left unused, will serve to show that in 

 former volumes of essays I have not too exhaustively 

 drawn upon the resources available to me. 



I have little to remark by way of preface on the contents 

 of the present volume. The opening essay touches 

 towards its close upon some considerations respecting the 

 Star-depths, which have been based on a long series of 

 original researches. These, as well as my independent in- 

 vestigation of the circumstances of the approaching transits 

 of Venus, will, in a very short time, be published in a 

 volume entitled * The Universe and the Coming Transits.' 



The second and third essays are more fanciful, perhaps, 

 than befits even the * Borderland of Science.' The reader 

 must regard them as merely indicating (so far as physical 

 phenomena are concerned) such circumstances as would, 

 in my opinion, be recognised by a being capable of 

 voyaging through the solar system. 



It appears to me that the considerations urged in the 

 essay upon Coal, respecting the exhaustion of the supply, 

 are sounder than those against which they are advanced. 

 In fact, although the essay is dated October 1872, when 



