vi PREFACE TO THE ENGLISH EDITION. 



The kindness of Mr. Stevenson lias enabled a reference 

 of some length to be made to the various systems of light- 

 house lenses which have been recently introduced. 



The Editor is also under obligation to Mr. MacDonald, the 

 Manager of the Times, for information regarding the Walter 

 Press and for the use of the woodcut by which its action 

 is made clear ; to Dr. Andrews for permission to include 

 in part his account of the principles involved in the con- 

 struction of the various Magneto-electric Machines; and to 

 Mr. Conrad Cooke for a description of the Electric Light 

 used in the Houses of Parliament. 



To Mr. Cunliffe Owen, the Director of the South 

 Kensington Museum, Messrs. Elliott, Shand and Mason, 

 Aveling and Porter, and Mr. Browning, the Editor is 

 indebted for the use of several illustrations. 



