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Preface

"... Mr. Hopkins was an expert mechanic.  One of his chief pleasures was to make experiments at his home in his well-equipped work-shop and laboratory, and the work described in the present volume is nearly all result of his experiments made by him during such "idle" hours. 

It has been the intention of the author to make the present work as suggestive as possible.  No complicated apparatus is required in carrying out the experiments described.  Any one with ordinary mechanical ingenuity and having a lathe and a few tools can make most of the experiments described in these pages."