10 INTRODUCTION 



in its passage the soft iron inclosed in the bobbins or electro- 

 magnets, which, after a series of movements which we can only refer 

 to now, acts each time the current passes over the tracing pencils 

 of the instruments. But chemical reaction gives birth to the in- 

 visible current; and a chemical reaction is produced at the end, and 

 a series of coloured points traces on the paper the very image of the 

 characters written at the point of departure. A drawing, plan, or 

 any figure, or shorthand signs can, of course, be also thus reproduced. 

 A thousand other curious inventions that which I have just 

 quoted is doubtless among the most striking have been realized from 

 the same principle : that of the action of electricity at a distance. 

 This force, the real nature of which is still unknown, and of which 

 three centuries ago the existence was scarcely dreamt of, which 

 before that time was only manifested under the form of thunder 

 this force has become, thanks to science, thanks to the experimental 

 investigations, and also and this we must emphasize thanks to 

 the indications of theory, the docile agent of man. It transmits 

 human thought to a distance, whether along aerial wires or 

 through cables which are immersed in the depths of the ocean ; 

 at a distance it sets fire to mines and torpedoes ; it is a light-source 

 which rivals the sun ; it transmits and regulates the movement of 

 clocks ; it melts metals ; it covers objects with an imperceptible 

 layer of a precious metal, gold, silver, or platinum; and, lastly, it 

 reproduces the works of the sculptor or the modeller. 



VI. 



To bring together in a single work all these many different 

 applications, to describe the instruments, machines, and apparatus 

 of all kinds, by the help of which inventors have succeeded in real- 

 izing them ; to make them easily understood, in principle if not 

 in detail, such is the aim proposed in this work. The various 

 chapters which compose it do not pretend to replace technical 

 manuals, by means of which each application is studied for practical 

 purposes. Besides, the idea of the book is far different, as I have 

 before stated. The present volume is the complement of the one 

 in which the phenomena and their laws have been studied. The 



