EDITOR'S INTRODUCTION.
The works to be comprised in this Series are intended 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 treatment, 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
