PREFACE TO FIRST EDITION. 



IN preparing these Essays, my chief object has been 

 to present scientific truths in a light and readable 

 form clearly and simply, but with an exact adherence 

 to the facts as I see them. I have followed here and 

 always the rule of trying to explain my meaning 

 precisely as I should wish others to explain, to my- 

 self, matters with which I was unfamiliar. Hence 

 I have avoided that excessive simplicity which some 

 seem to consider absolutely essential in scientific essays 

 intended for general perusal, but which is often even 

 more perplexing than a too technical style. The chief 

 rule I have followed, in order to make my descriptions 

 clear, has been to endeavour to make each sentence 

 bear one meaning, and one only. Speaking as a 

 reader, and especially as a reader of scientific books, I 

 venture to express an earnest wish that this simple 

 rule were never infringed, even to meet the require- 

 ments of style. 



It will hardly be necessary to mention that several 

 of the shorter Essays are rather intended to amuse 

 than to instruct. 



