DOVE ON THE ELECTRICITY OP INDUCTION. 159 



the first, and which, by means of a sliding board, could be 

 brought to any requisite distance from it. This spiral B^ was 

 connected with the two inner cylindrical spirals a b and c c? of 

 the differential inductor for frictional electricity (fig, 3), which 

 on the discharge of the battery induced in the outer spirals ajB 

 and 7 S, which were connected in a uniform manner, a current 

 of the third order, the physiological action of which could be 

 tested when a b and c d were empty, or when they contained 

 iron. Lastly, that case was examined in which the primary cur- 

 rent was that of a Saxton's machine. The wire coils of this in- 

 strument (fig. 7) were connected with a spiral A^^ 400' long, 

 which exerted an inducing action upon a coil of wire B^^ 400' 

 long, into which it was inserted. This first outer spiral B^^ was 

 connected with an inner one C^, 400' long, and corresponding 

 completely with A^,, which exerted an inducing action upon a 

 second outer spiral D,,, which entirely corresponded to B^^. The 

 current of this spiral Dy, was tested when C^, contained iron, or 

 when it was empty. 



The result of these experiments was, that these second in- 

 duced currents, or as Henry calls them, the currents of the third 

 order, behave as the currents of the second order, which give rise 

 to them, i. e. the currents whose primary current was excited by 

 machine electricity were weakened by solid iron, and on the 

 contrary, their power was increased by bundles of iron wires; 

 whilst those induced by galvanic agency were increased in power 

 by both, but by bundles of wires more than by iron rods. The 

 same applies to the currents of the third order from Saxton's 

 machine. 



2. Currents of higher orders when the first induced current is a 

 magneto-electric current. 



67. If iron is already present in the connecting spiral A of 

 the galvanic battery or of the Leyden jar, then the first induced 

 current is not alone produced by electro-dynamic agency, but is 

 chiefly excited by the evanescent magnetism of the electro-mag- 

 netized iron. If the magneto-electric portion of the current is 

 to be employed alone as the primary current for the currents of 

 higher orders, then the galvanic battery or the electric battery 

 must be closed by a differential inductor, only one of the spirals 

 of which must contain iron. The current then induced by it 

 exerts an inducing action upon the adjacent spiral. If the 



