OP THE LATE MR. WILLIAM STURGEON. 59 



new field of investigation thereby opened. Davy and Arago 

 magnetized steel needles, by placing them in the vicinity of 

 a wire carrying a voltaic current. Ampere found that two 

 parallel wires conveying currents in the same direction attracted 

 one another, but that they repelled one another if the elec- 

 tricity travelled in contrary directions ; and Faraday produced 

 the revolution of a magnetic bar round a conducting wire, as 

 well as the reverse phenomenon of the revolution of a con- 

 ducting wire round one of the poles of a magnet. 



Mr. Sturgeon followed in the same track, and the mechanical 

 skill he possessed enabled him to construct and improve the 

 beautiful revolving apparatus, which had been devised by 

 Faraday, Barlow, Ampere, and others. The rotations are in 

 all cases owing to the action of a wire carrying a current of 

 electricity, upon either a permanent magnet or another electro- 

 dynamic wire, and may in every case be traced to Oersted's 

 law. Considerable instruction may, however, be derived from 

 their study, and it would appear that they were the object of 

 Mr. Sturgeon's earliest scientific efforts. We accordingly find 

 in the London Philosophic&l Magazine for September, 1823, 

 an account of his modification of Ampere's rotating cylinders. 

 This contrivance is succinctly described by Mr. Jones, optician, 

 as " consisting of two sets of revolving cylinders, one suspended 

 on each pole of an inverted horse-shoe magnet. Upon the 

 insertion of dilute nitric acid the two sets of cylinders simulta- 

 neously enter into rotations, in a very interesting and striking 

 manner." The effect, adds the same authority, is the most 

 pleasing I have ever seen. 



In 1824 Mr. Sturgeon published four papers on thermo- 

 electricity, in which he succeeded in giving a fresh proof of 

 the complete analogy which subsists between thermo-electric 

 and voltaic currents. 



In 1825 he presented to the Society of Arts the complete 

 set of novel electro-magnetic apparatus, which is described 

 in their transactions. The great merit of this collection con- 



