PROLOGUE 



[Controverted Questions, 1892] 



Le plus grand service qu'on puisse rendre a la science est d'y 

 faire place nette avant d'y rien construire. CUVIER. 



MOST of the Essays comprised in the present 

 volume have been written during the last six or 

 seven years, without premeditated purpose or 

 intentional connection, in reply to attacks upon 

 doctrines which I hold to be well founded ; or in 

 refutation of allegations respecting matters lying 

 /within the province of natural knowledge^ which I 

 believe to be erroneous ; and they bear the mark 

 of their origin in the controversial tone which 

 pervades them. 



Of polemical writing, as of other kinds of war- 

 fare, I think it may be said, that it is often useful, 

 sometimes necessary, and always more or less of 

 an evil. It is useful, when it attracts attention to 

 topics which might otherwise be neglected; and 

 when, as does sometimes happen, those who come 

 to see a contest remain to think. It is necessary, 



