Silvanus P. Thompson 
Elementary Lessons in Electricity Magnetism [PDF ebook] 

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. The author returns cordial thanks to various professional friends and electrical engineers who have aided him with information. He has to thank Dr. C. Chree, of the Kew Observatory, for sundry magnetic data, and Professor L. A. Bauer, of Washington, for material used in preparing the magnetic map of North America.