Few men of the nineteenth century are so interesting as André Marie Ampère, who is, as we have seen, deservedly spoken of as the founder of the science of electro-dynamics. Extremely precocious as a boy, so that, like his immediate predecessor in discovery, Oersted the Dane, his rapid intellectual development drew down upon him ominous expressions from those who knew him, he more than fulfilled the highest promise of his early years. His was no one-sided genius. He was interested in everything, and his memory was as retentive as his intellect was comprehensive. He grew up, indeed, to be a young man of the widest possible interests. Literature never failed to have its attraction for him, though science was his favorite study and mathematics his hobby. The mathematical mind is commonly supposed to run in very precise grooves, yet Ampère was always a speculator, and his speculations were most suggestive for his contemporaries and subsequent generations. Indeed, his mathematics, far from being a hindrance to his penetrating outlook upon the hazier confines of science, rather seemed to help the penetrations it gave. While he was so great a scientist that Arago, so little likely to exaggerate his French contemporary's merit, has said of Ampère's discovery identifying magnetism and electricity, that "the vast field of physical science perhaps never presented so brilliant a discovery, conceived, verified, and completed with such rapidity," his friends knew this great scientist as one of the kindliest and most genial of men, noted for his simplicity, his persuasive sympathy and his tender regard for all those with whom he was brought into intimate relations. [Illustration: ANDRÉ MARIE AMPÈRE] The commonly accepted formula for a great scientist, that he is a man wrapt up in himself and his work, enmeshed so completely in the scientific speculations that occupy him that he has little or no time for great humanitarian interests, so that his human sympathies are likely to atrophy, is entirely contradicted by the life of Ampère. He was no narrow specialist, and, indeed, it may be said that not a single one of these great discoverers in electricity whom we are considering in this volume was of the type that is sometimes accepted as indicative of scientific genius and originality. After reading their lives, one is prone to have the feeling that men who lack that wider sympathy which, in the famous words of the old Latin poet, makes everything human of interest to them, are not of the mental calibre to make supreme discoveries, even though they may succeed in creating a large amount of interest in their scientific speculations in their own generation. It is the all-round man who does supreme original work of enduring quality.