328 PROGRESS IN PHYSICS. 



sai'ily postponed until a second capital disco veiy camo to remove most 

 of the difficulties. 



This was the discovery of a relation between electricity and. mag- 

 netism, the existence of which had long been suspected and earnestly 

 sought. A Danish professor, Hans Christian Oersted, was fortu- 

 nate in hitting upon an experiment which demonstrated this relation 

 and opened up an entirely new field of investigation. What Oersted 

 found was that when a conductor, as a copper wire, carrying an elec- 

 tric current was brought near a freely suspended magnet, like a com- 

 pass needle, the latter would take up a definite position with reference 

 to the current. Thus an electric current moved a magnet, and acted like 

 a magnet in producing a ''magnetic field." The subject was quickly 

 taken up by almost every physicist in Europe and America. Arago 

 found that iron tilings would cling to a wire through which a current 

 was passing, and he was al)le to magnetize steel needles by means of 

 the current. Ampere, another French physicist, studied Oersted's 

 wonderful discovery both experimentally and mathematically and in 

 an incredibly short time so developed it as to deserve the title of cre- 

 ator of the science of electro-dynamics. 



The first to make what is known as an electro-magnet was an Eng- 

 lishman named Sturgeon, who used a bar of soft iron bent in a horse- 

 shoe form (as had long been common in making permanent steel mag- 

 nets), and after varnishing the iron for insulation wrapped a single coil 

 of copper wire about it through which the current from a battery was 

 passed. There were thus two ways of producing visible motion by 

 means of an electric current, that of Oersted's simple experiment, in 

 which a suspended magnetic needle was deflected b}^ a current, and 

 that made possible ))v the production, at will, of an electro-magnet. 

 The application of both of these ideas to the construction of an electric 

 telegraph was quickW attempted, and two difierent systems of teleg- 

 raphy grew out of them. One, depending on Oersted's experiment, 

 was developed in England first and afterwards in Europe; the other, 

 that involving the use of signals produced b}^ an electric magnet, was 

 developed in America and was generally known as the American 

 method. It has long ago superseded the first method in actual prac- 

 tice. Its possibility depended on perfecting the electro-magnet and 

 especially on an understanding of the principles on which that per- 

 fecting depended. For the complete and satisfactory solution of this 

 problem we are indebted to the most famous student of electricity 

 America has produced during the century, Joseph Henry. 



In 1829, while a teacher in the academj'^ at Albany, N. Y., Henry 

 exhibited an electro-magnet of enormously greater power than any 

 before made, involving all of the essential features of the magnet of 

 to-day. The wire was insulated by silk wrapping, and many coils were 

 placed upon the iron core, the intensity of magnetization l)eiiag thus 



