IV PREFACE 



I know by large experience that these are the bugbear of 

 the ordinary reader, for whom this volume is specially in- 

 tended. Therefore I have endeavored to state everything 

 in such a simple manner that any one with a mere common 

 school education can understand it. This, I trust, will ex- 

 plain the absence of everything which requires the use of 

 anything higher than the simple rules of arithmetic and the 

 most elementary propositions of geometry. And even this 

 I have found to be enough for many lawyers, physicians, 

 and clergymen who, in the ardent pursuit of their profes- 

 sions, have forgotten much that they learned at college. 

 And as I hope to find many readers amongst intelligent 

 mechanics, I have in some cases suggested mechanical 

 proofs which any expert handler of tools can easily carry 

 out. 



As a matter of course, very little originality is claimed 

 for anything in the book, the only points that are new 

 being a few illustrations of well-known principles, some of 

 which had already appeared in " The Young Scientist " and 

 " Self-education for Mechanics." Whenever the exact 

 words of an author have been used, credit has always 

 been given ; but in regard to general statements and ideas, 

 I must rest content with naming the books from which I 

 have derived the greatest assistance. Ozanam's " Recrea- 

 tions in Science and Natural Philosophy," in the editions 

 of Hutton (1803) and Riddle (1854), has been a storehouse 

 of matter. Much has been gleaned from the " Budget of 

 Paradoxes " by Professor De Morgan and also from Profes- 

 sor W. W. R. Ball's " Mathematical Recreations and Prob- 

 lems." Those who wish to inform themselves in regard to 

 what has been done by the perpetual -motion -mongers must 

 consult Mr. Dirck's two volumes entitled "Perpetuum 



