DYNAMO-ELECTRIC MACHINES. 85 



may be driven by the same kind of motor. Viewed in this way each 

 type can be called by either name. The object of Dr. Siemens, how- 

 ever, was to distinguish one class of machines, which converted 

 mechanical force into electricity, and were self-exciting, from the other 

 class, which converted force into electricity, by the inductive action 

 of permanent magnets only. Paccinotti, an Italian-Frenchman, or a 

 French-Italian, was one of the first in the field with a Dynamo 

 machine. And it is in some measure to him that M. Gramme is 

 indebted for the type of machine that bears his name. There are 

 but two distinctive types of continuous current machines, although 

 there are many modifications of each. That of Gramme has its 

 armature wound round the outside and through the inside. It is in 

 fact a broad ring composed of many turns of iron wire bent flatways 

 in cylindrical form with the turns of the many coils, of which it is 

 composed, wound around and around it. The Maxim, Fuller, and 

 Brush in America are more or less modified types of the Gramme. 

 The other distinctive type is the Siemens, differing only from the 

 Gramme, in the winding of its armature, which, instead of being a 

 ring, is a cylinder with the wire wound lengthwise on the outside, 

 altogether. The wire begins at one end of the cylinder, is passed 

 lengthwise along the face, crosses over the end, and is bent aside to 

 clear the axis or shaft. It is carried in the opposite direction to the 

 other end of the cylinder, which it crosses in the same manner, and 

 is so wound until the section is completed. The types of this 

 machine made on this continent, are the Edison, Weston, and some 

 others. The Wallace-Farmer machine is a modification of Wilde's 

 bobbin machine, and is composed of a number of bobbins (in form 

 like the segment of a circle with rounded ends) each having a separate 

 and distinct core, all of which are attached to the disc. Two discs, 

 with bobbins so attached, are placed side by side on the same shaft, 

 so that they are in reality two machines in one. There is another 

 class of machines called alternate current machines, which have a 

 number of north and south poles, alternating with each other, and 

 which give rise to as many currents alternating in direction ; that is, 

 a momentary current is sent through the conductor, say, in a positive 

 direction, and on the passage of the bobbin giving birth to this 

 current before a pole of opposite magnetism, a negative current is 

 sent through the circuit and so on all around the machine. There 



