viii PREFACE. 



various sciences, by means of which questions can be 

 framed, either upon the discoveries of any given 

 period, or on the progressive advance, through several 

 centuries, of any of the five main divisions of science 

 which are dealt with in this volume. 



In conclusion, I wish to acknowledge my obliga- 

 tions to many kind friends, and especially to Mr. A. 

 R. Wallace and Mr. J. C. Moore, F.R.S., who have 

 rendered me very material and valuable assistance. 

 I am also much indebted to the Rev. R. M. Luckock, of 

 the Godolphin Grammar School, who read the whole 

 work in manuscript, with a view to pointing out any 

 portions which might be unintelligible to schoolboys. 



LONDON : December 1875. 



