EDITOR'S INTRODUCTION. 



The works to be comprised in this Series are in- 

 tended to give on each subject the information which an 

 intelligent layman might wish to possess. They are not 

 primarily intended for the young, nor for the specialist, 

 though even to him they will doubtless be often useful 

 in supplying references, or suggesting lines of research. 



Each book will be complete in itself, care, however, 

 being taken that while the books do not overlap, they 

 supplement each other ; and while scientific in treat- 

 ment, they will be, as far as possible, presented in 

 simple language, divested of needless technicalities. 



The rapid progress of science has made it more and 

 more difficult, and renders it now quite impossible, to 

 master the works which appear, almost daily, on various 

 branches of science, or to keep up with the proceedings 

 of our numerous Scientific Societies. 



A distinguished statesman has recently expressed 

 the opinion, that we cannot expect in the next fifty 

 years any advance in science at all comparable to that of 

 the last half-century. Without wishing to dogmatise, I 



