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law of simple harmonic motion. He was 

 aware that there were great difficulties in 

 treating it in any other way. First of all 

 the law itself had to be found ; and 

 secondly, he did not know of any graphic 

 method of solving the problems when 

 the law had been found. The analytical 

 method was probably even more difficult. 

 It was generally complicated enough 

 even with a simple harmonic law, but 

 with irregular laws he did not know that 

 it could be touched at all. He had 

 therefore brought a diagram showing 

 what were likely to be the errors even in 

 the machines the author had treated of, 

 taking the harmonic law to be true. In 

 Figs. 29, the curves 1, 2, and 3 showed 

 the primary electromotive force induced 

 in a coil all wound in a single line on the 

 armature, by moving it through three 

 different forms of magnetic field, a har- 

 monic field, a field such as occurred in 

 the Mordey machines, and a field such as 

 was given by the author's machine with 

 opposite poles alternately on each side 

 of the ring, with a space equal to the 



