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HE demand for another edition of the present work first issued in 1876 is very gratifying to the author. The chief additions in the present edition consist of articles upon the Magnetic Circuit and on the Dynamo. Having worked through the book in recent years with his pupils the author has learnt how much inaccuracy, obscurity and inadequacy of explanation remained even in the last issue, and he has spared no pains to remove such blemishes in the present edition. He also takes the opportunity of thanking numerous friends both at home and in America for sending him frequent communications concerning one part and another of the book, all of which have received careful consideration.
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