180 Mr. H. Pender on the Magnetic 



The conclusion is in direct opposition to the classical experi- 

 ment performed by Professor Rowland * in Berlin, in 1876, 

 which was subsequently repeated in this laboratory by Pro- 

 fessor Rowland and C. T. Hutchinson f in 1889, and confirmed 

 also by experiments performed by Rontgen J and Himstedt § 

 in Germany. A further investigation of this very important 

 question was therefore considered desirable. Accordingly 

 in the fall of 1900, under the supervision of Professor 

 Rowland, the following research was undertaken. As a result, 

 it has been shown conclusively that electrical convection 

 does produce magnetic action. 



The idea that a moving electrified body might produce a 

 magnetic effect similar to that produced by an electric current 

 first occurred to Faraday || in 1837. The first to perform 

 an actual experiment on the subject, however, was Professor 

 Rowland. The experiment was carried out in Germany in 

 1876, though the idea of it had occurred to him as early as 

 1868, and is recorded in a note-book of that date. His 

 method was similar to that described by Maxwell in his 

 Treatise on Electricity and Magnetism (§ 770), written pre- 

 sumably in 1872 or 1873. 



In the Berlin experiment, Professor Rowland used a 

 horizontal hard-rubber disk (diameter 21. cm.), coated on 

 both sides with gold, revolving between two glass plates with 

 their inner surfaces also gilded. Each side of the disk 

 formed a condenser with the gilded surface opposite it. The 

 condensing plates were earthed ; and the disk charged by 

 means of a point brought up within -J- mm. from the 

 periphery. An astatic needle was suspended above the upper 

 condensing plate, so that its lower magnet was nearly over 

 the edge of the disk, and perpendicular to a radius of the 

 sume. The needle was inclosed in a metal case, so as to 

 screen it from electrostatic action. The speed of the disk 

 was 61 revolutions per second. On reversing the sign of 

 electrification of the disk, a deflexion of from 5 to 7*5 mm. 

 was obtained, depending on the conditions. The deflexion 

 was the same whether the gilded surfaces of the disk and 

 condensing plates were divided into sectors, or left continuous. 

 The deflexion as observed and calculated agreed quite well, 

 but as the needle was always very unsteady, it was impossible 

 to make the readings with any great accuracy. In 1883 



* Pogg. Ann. clviii. p. 487; Am. Journ. Sci. 1878, p. 30. 

 t Phil Mag. xxvii. p. 445 (1889). 

 J Ber. d. Berl. Akad. 1885, p. 195. 

 § Wied. Ann. xxxviii. p. 560 (1889). 

 |l Exp. lies. vol. i. art. 1644. 



