10 Professor Tyndall [Jan. 17, 



But the discovery which, above all others, brought the practical 

 question to the front is now to be considered. On the 4th of 

 February, 1867, a paper was received by the Eoyal Society from 

 Dr. William Siemens bearing the title, " On the conversion of Dynamic 

 into Electrical Force without the use of Permanent Magnetism." * 

 On the 14th of February a paper from Sir Charles Wheatstone was 

 received, bearing the title, " On the augmentation of the Power of a 

 Magnet by the reaction thereon of Currents induced by the Magnet 

 itself." Both papers, which dealt with the same discovery, and which 

 were illustrated by experiments, were read upon the same night, viz. on 

 the 14th of February. It would be difficult to find in the whole field 

 of science a more beautiful example of the interaction of natural 

 forces than that set forth in these two papers. You can hardly find 

 a bit of iron — you can hardly pick u-p an old horse-shoe, for example 

 — that does not possess a trace of permanent magnetism ; and from 

 such small beginnings Siemens and Wheatstone have taught us to 

 rise by a series of interactions between magnet and armature to a 

 magnetic intensity previously unapproached. Conceive the Siemens' 

 armature placed between the poles of a suitable electro-magnet. 

 Suj)j)ose this latter to possess at starting the faintest trace of 

 magnetism ; then when the armature rotates, currents of infini- 

 tesimal strength are generated in its coil. Let the ends of that coil 

 be connected with the wire surrounding the electro-magnet. The 

 infinitesimal current generated in the armature will then circulate 

 round the magnet, augmenting its intensity by an infinitesimal 

 amount. The strengthened magnet instantly reacts upon the coil 

 which feeds it, producing a current of greater strength. This current 

 again passes round the magnet, which immediately brings its enhanced 

 power to bear upon the coil. By this i)lay of mutual give and take 

 between magnet and armature, the strength of the former is raised 

 in a very brief interval from almost nothing to complete magnetic 

 saturation. Such a magnet and armature are able to produce currents 



was briefly expressed in a report to the Elder Brethren of the Trinity House on 

 the ITtli of May, 1866 : " It gives me pleasure to state that the machine is 

 exceedingly effective, and that it far transcends in power all other apparatus of 

 the kind." 



* A paper on the same subject, by Dr. Werner Siemens, was read on the 17th 

 of January, 1867, before the Academy of Sciences in Berlin. In a letter to 

 ' Engineering,' No. 622, p. 45, Mr. Eobert Salnnc states that Professor Wheat- 

 stone's machines were constructed by Mr. Stroh in the months of July and 

 August, 1866. I do not doubt Mr. Sahine's statement ; still it would be dan- 

 gerous in the highest degree to depart from the canon, in asserting which 

 Faraday was specially strenuous, that the date of a discovery is the date of its 

 publication. Towards the end of December, 1866, IMr. Alfred Varley also lodgal 

 a provisional specification (vvliich, I believe, is a sealed document) embodying the 

 principles of the dynamo-electric machine, but some years elapsed before he made 

 anytliing public. His brother, Mr Cromwell Varley, when writing on this subject 

 in 1867, dots not mention him ('Proc. Roy. Soc,,' March 14, 1867). It probably 

 marks a national trait that sealed communications, thougli allowed in France, 

 have never been recognized by the scientific societies of England. 



