PREFACE BY THE EDITOR. v 



been an object, so that a repetition of reference to the same work has 

 been, as much as possible, avoided. Thus most of the works which are 

 mentioned under one branch of the mechanical sciences, embrace many 

 others under which they are not quoted. For example, the autho- 

 rities on central forces (Lect. IV.) do not include Laplace, Lagrange, 

 and others, because these authors have been already given in Lect. II., 

 as treating on a branch of the same subject. This want of repetition 

 may be considered a defect, but it must be remembered, that the cata- 

 logue has already extended to several thousand articles. On the 

 whole, it is expected that this edition will supply a work greatly 

 needed, in which correct exposition is combined with extensive 

 research. 



Great pains have been taken to render the Table of Contents and 

 Index as complete and accurate as possible. In framing these, the 

 Editor has received the valuable assistance of Mr. Stewart, which he 

 begs thankfully to acknowledge. 



