IV PREFACE. 



With the faint hope that I would have no difficulty in 

 simply retaining the text that helps to explain the in general 

 excellent woodcuts that illustrate the present volume, I 

 undertook to revise it. Those familiar with the subject will 

 perhaps appreciate the statement that, as it proved, it would 

 have been an easier and certainly a more pleasant task to 

 have re-written the work. Those who will compare the 

 present edition with that of 1869, will see that the alterations 

 in this one have been very numerous and important, several 

 chapters being nearly re-written ; that all the dogmatic asser- 

 tions, so striking in the edition of 1869, have been toned down 

 in conformity with that modesty that should characterise the 

 searchers after truth ; and that the more rampant twigs of 

 French eloquence have been pruned in conformity with our 

 quieter if not better taste. Would that I could add that they 

 will also find all errors corrected, but of the contrary I am 

 painfully aware. At the same time, I believe the candid 

 critic will see that if in this matter I have not done all I 

 should, I have at least, under all the circumstances, done all 

 I could. 



I am indebted to my friend, G. J. Stoney, M.A., F.R.S., 

 for the short account of the cause of the tides, to be found 

 on pages 32 to 35. Perhaps never before has the subject 

 been treated in a more popular and yet scientific a way. 



E. P. W. 



n . 



