THE DEVELOPMENT OP ELECTRICAL SCIENCE. 221 



given by Boinagnesi in a work published in 1805, but little or no notice 

 appears to have been taken of this. Certainly no progress was made 

 in the subject till 1820, when Oersted made his famous experiment 

 before his class. By that experiment he proved that a wire carrying 

 an electric current will, when properly placed, deflect a magnetic 

 needle. The subject was almost immediately taken up by Ampere, and 

 in a few months many of the important consequences which Oersted's 

 discovery involved were developed. Ampere's work on the action of 

 currents on currents and on magnets is classical and is still treated as 

 part of the fundamental basis for the theory of electrodynamics. An 

 account of his work may therefore be found in almost any of the nu- 

 merous text-books on electricity. The conclusions reached by Ampere 

 were confirmed by Weber by a series of much more refined experiments. 

 To Weber also we owe improvements in galvanometers. The same 

 year marks the discovery by Arago that a current can not only deflect 

 a magnet, but that it is capable of producing one by magnetizing steel 

 needles. 



The further discovery was made four years later by Sturgeon that 

 soft iron, although incapable of making a strong permaneut magnet, is 

 yet much more susceptible than steel to temporary magnetization by 

 the electric current. Arago also made about this time the important 

 discovery that if a needle be suspended above a copper disc and the 

 disc rotated the needle will be dragged round with the disc. This was 

 not explained for some years, but seems to be the first discovery of 

 induced currents. 



These experiments mark the discovery of electro-magnetism, and 

 began one of the most important eras in electrical discovery, the work 

 which has been participated in by many eminent authorities. Among 

 the many advances may be mentioned the experiments of Henry on the 

 relative effects of different windings on the strength of an electro- 

 magnet. He deduced the fact that the magnetizing action might be 

 increased either by increasing the number of windings, the current 

 remaining the same, or by increasing the current, the winding remain- 

 ing the same. He pointed out the application of this to intensity and 

 quantity arrangements of the battery, and also the importance of the 

 intensity winding for the transmission of magnetizing power to a dis- 

 tance, as in telegraphy. The increased effect due to increasing the 

 number of windings on the coil of a galvanoscope had been previously 

 pointed out by Schweigger, and the discovery is embodied in Schweig- 

 ger's galvanoscope. 



In 1821 Faraday began his researches and many inportant discov- 

 eries were made by him. The main guiding idea in Faraday's work 

 was the possibility of obtaining electricity from magnetism and in gen- 

 eral the discovery of the interrelation between the two. In this con- 

 nection Arago's discovery of the rotation of a copper disc by the rota- 

 tion of a magnet above it is of great importance, because, among other 



