282 Chronicles of Science. [April, 



TyndalTs ' Heat as a Mode of Motion ' (and we hope soon to add 

 to these the volumes of Sir William Thompson and Professor Tait 

 on " Natural Philosophy.'' promised for this series ). the student of 

 this year will possess advantages which have never before fallen to 

 the lot of any one whose object is to acquire a thorough knowledge 

 of physics. 



Electricity. — Two very important papers on Electricity were 

 presented to the Pioyal Society on February 14th. They are on 

 almost the same subject, and are interesting, as showing how the 

 same idea in the minds of two profound electricians becomes 

 developed into an important discovery, — alike as far as the principle 

 is concerned, but widely differing in ultimate results, and in the 

 instrumental means adopted to obtain the desired end. 



The first paper was by C. W. Siemens, F.Pi.S., "On the Con- 

 version of Dynamical into Electrical Force, without the aid of 

 permanent Magnetism." The apparatus employed in this experi- 

 ment was an electro-magnetic machine •consisting of one or more 

 horseshoes of soft iron, surrounded with insulated wire, in the usual 

 manner ; of a rotating keeper of soft iron, surrounded also with an 

 insulated wire ; and of a commutator connecting the respective coils 

 in the manner of a magneto-electrical machine. If a galvanic bat- 

 tery were connected with this arrangement, rotation of the keeper 

 in a given direction would ensue. If the battery were excluded 

 from the circuit, and rotation imparted to the keeper in the oppo- 

 site direction to that resulting from the galvanic current, there 

 would be no electrical effect produced, supposing the electro-magnets 

 were absolutely free of magnetism ; but by inserting a battery of a 

 single cell in the circuit, a certain magnetic condition would be set 

 up, causing similar electro-magnetic poles to be forcibly severed, 

 alternately, the rotation being contrary in direction to that which 

 would be produced by the exciting current. 



Instead of employing a battery to commence the accumulative 

 action of the machine, it sufficed to touch the soft iron bars employed 

 with a permanent magnet, or to dip the former into a position pa- 

 rallel to the magnetic axis of the earth, in order to produce the same 

 phenomenon as before. Practically it was not even necessary to 

 give any external impulse upon restarting the machine, the resi- 

 duary magnetism of the electro-magnetic arrangements employed 

 being found sufficient for that purpose. 



The mechanical arrangement best suited for the production of 

 these currents was that originally proposed by Br. Werner Siemens 

 in 1857, consisting of a cylindrical keeper, hollowed at two sides, 

 for the reception of insulated wire, wound longitudinally, which 

 was made to rotate between the poles of a series of permanent 

 magnets, which latter were at present replaced by eleetro-niagnets. 



