62-i ADDITIONS. 



thither in an imperceptible time ; and by means of well-devised sys- 

 tems of operation, is made to convey from man to man words, which 

 are now most emphatically " winged words." In the most civilized 

 states such wires now form a net-work across the land, which is fami- 

 liar to our thoughts as the highway is to our feet ; and wide seas have 

 such pathways of human thought buried deep in their waves from 

 shore to shore. Again, by using the chemical effects of electrodyna- 

 mic action, of which we shall have to speak in the next Book, a new 

 means has been obtained of copying, with an exactness unattainable 

 before, any forms which art or nature has produced, and of covering 

 them with a surface of metal. The Electrotype Process is now one of 

 the great powers which manufacturing art employs. 



But these discoveries have also been employed in explaining natural 

 phenomena, the causes of which had before been altogether inscruta- 

 ble. This is the case with regard to the diurnal variation of the mag- 

 netic needle ; a fact which as to its existence is universal in all places, 

 and which yet is so curiously diverse in its course at different places. 

 Dr. Faraday has shown that some of the most remarkable of these 

 diversities, and probably all, seem to be accounted for by the different 

 magnetic effects of air at different temperatures : although, as I have 

 already said, [Book xii.) the discovery of a decennial period in the 

 diurnal changes of magnetic declination shows that any explanation of 

 those changes which refers them to causes existing in the atmosphere 

 must be very incomplete. 15 



18 Researches, Art. 2892. 



