PREFACE. 



experiment illustrated will often depend on 

 the fact that this object is in view. 



In both kinds of paradox, the desire to 

 gratify curiosity by seeking the explanation 

 will promote an interest in the intelligent study 

 of the workings of natural forces ; and this is 

 no less truly the study of science than much 

 of the rote-work for examinations which is 

 done under that name. 



W. H. 



