Magneto-Electricity, and Electro-magnetical Machines. 125 



Art. X. — Prof. Locke on Magneto-Electricity, and Electro- 

 magnetical Machines. 



Med. Coll. of Ohio, Jan. 28th, 1838. 



TO PROF. SILLIMAN. 



Dear Sir — I mentioned to you in my last letter, some experi- 

 ments which I was about to make in Magneto-Electricity ; I have 

 now finished one series of them, part of which I propose to com- 

 municate to the public through your Journal. As it is possible, 

 that some of your readers may not be sufficiently acquainted with 

 the principles of magneto-electricity, to understand fully the ap- 

 paratus and experiments which I am about to describe, I will take 

 the liberty to prefix a concise statement of a few of the most im- 

 portant elementary principles. 



1. Whenever a permanent steel magnet or loadstone attracts a 

 piece of soft iron, it converts that iron into a magnet, so long only 

 as it attracts it, with poles opposite in their character to those by 

 which they are attracted. This takes place when the horse-shoe 

 magnet attracts its " keeper." 



2. If the soft iron, thus made magnetical by the attraction of a 

 permanent magnet, be forced off and reversed in position, its po- 

 larity or magnetism will be reversed. 



3. If the " keeper," or soft iron attached to the magnet be wrap- 

 ped by an insulated coil or " helix" of copper wire, as a spool is 

 wrapped by its thread, and be applied to, or detached from, the 

 permanent magnet, or be reversed in position so as suddenly 

 to acquire, lose, or change polarity ; electricity, at the moment 

 of change, will pass through the coil with its usual character- 

 istics. 



4. If the end of a bar magnet be thrust within a coil, or with- 

 drawn from it, an electrical current will be momentarily excited. 

 (Faraday.) 



5. Even the feeble polarity excited by terrestrial magnetism 

 on placing a bar of soft iron perpendicularly, and suddenly rever- 

 sing it, is attended by a sensible evolution of electricity in a coil 

 surrounding that bar. The experiment succeeds still better, by 

 making it in the line of the " dip," viz. with the upper end inchned 

 about 20° to the south. 



