66 MACHINES. 



would carry us beyond our limits, were we to attempt to describe 

 the beautiful experiments by which that philosopher was enabled 

 to prove the fact ; suffice it to say, that on this principle have 

 been constructed machines, by which a current of electricity is 

 set in motion without the aid of a battery. The general form 

 of one of these instruments is seen in the accompanying figure* 

 It consists of a horse-shoe magnet, which p- jg 

 is fixed to a frame ; opposite its poles is 

 placed what is termed the armature, which 

 can be rapidly revolved by means of a multi- 

 plying wheel. The armatures are nothing 

 more than electro-magnets, such as we have 

 already described; and by means of the 

 wheel, each pole of the armature is brought 

 in rapid succession opposite each pole of 

 the magnet, and that as nearly as possible 

 without touching; and a most brilliant succsesion of sparks, 

 forming almost a continuous light, is produced. The shocks 

 from these machines too, are very powerful ; but as it is a mat- 

 ter of no inconsiderable difficulty to regulate them according 

 to the necessity of the case, the use of the Magneto-Electric 

 Machines in medicine is very limited. 



CHAPTER VI. 



ON THE DETECTION OF NEEDLES AND OTHER 

 STEEL INSTRUMENTS IMPACTED IN THE BODY, 

 BY ELECTRO-MAGNETS. 



BEFORE bringing this little work to a conclusion, it is deemed 

 necessary to draw attention to a most valuable and important 

 application of the principles of electro-magnetism, recently 

 proposed by Mr. Alfred Smee. Every medical practitioner 



