PREFACE TO FOURTH EDITION. 



In the revision for this edition an effort has been 

 made to reach greater conciseness in the explanations 

 and in paragraphing the instructions in the use of 

 various kinds of apparatus. Many of the illustrations 

 have been replaced by new ones, and others have been 

 added. 



This book has been adopted in many schools as a 

 text book and it is hoped that its usefulness in this 

 direction may be extended. 



THE AUTHOR. 

 October, 1901. 



VII 



