supet-ior to any hitlm'to made. 259 



electro-magnet ; nor did it, even when the battery was small, 

 produce any sensible improvement in the action of the contact 

 breaker if the connexion with the battery was made and broken 

 by mercury and an amalgamated metal. This is an additional 

 proof of the superiority of the contact breaker in which mercury 

 and amalgamated copper are employed for making and breaking 

 contact. For, the only reason we can conceive why the con- 

 denser should produce a sensible improvement in all contact 

 breakers except the one in which mercury and an amalgamated 

 metal are used, is, that in this, the amalgamated metal makes 

 more perfect contact with mercury than platina does, or than two 

 solid metals make with each other, and therefore produces greater 

 magnetic power in the electro-magnet. 



The increased action produced by the condenser in various 

 contact breakers is a confirmation of the truth of the explanation 

 of the action of the condenser which is given in the paper I read 

 at the last meeting of the British Association, and which was 

 published in the Philosophical Magazine for last November. In 

 that paper I showed that the effects of the condenser are, — 1st, to 

 accelerate the motion of the electricity flowing in the primary 

 coil at the moment its connexion with the battery is broken, 

 and thereby increase the magnetic power of the core; and 

 2ndly, to destroy more suddenly the magnetism of the core 

 by the electrical current which rushes from the positive to the 

 negative plate of the condenser, as soon as the former receives 

 all the electricity flowing in the primary coil at the moment its 

 connexion with the battery is broken. These are precisely the 

 effects which I have found the condenser to produce on the elec- 

 tro-magnet of the contact breaker. 



I may mention here, that I have found by experiment that iron 

 wire coiled round the primary wire of an induction coil resists 

 the force with which electricity is attracted to the positive plate 

 of the condenser after the connexion between the primary wire 

 and battery is broken, and consequently that the immense quan- 

 tity of iron wire wound round the conducting wire of the Atlan- 

 tic cable must give great resistance to the electric current by 

 which messages are to be sent across the Atlantic. Hence, if 

 any other means can be employed to protect and strengthen the 

 conducting wire, it should be adopted in the part of the cable 

 which is not yet made, and the use of iron wire should be aban- 

 doned. 



Maynooth College, 

 Feb. 27, 1858. 



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