superior to any hitherto made. 257 



capable of giving to them. If the armature be drawn to the 

 poles of the electro-magnet through the g^^th of an inch, the 

 amalgamated piece of copper, being at 6 inches from the centre 

 of motion, will ascend ^th of an inch, and will be raised out of 

 the mercury even when the armature does not vibrate through 

 a distance greater than the y^-^th of an inch. The vibrations 

 through so small a distance are very rapid, and consequently the 

 connexion of the coil of the magnet, and of the primary wire 

 of the induction cod, with the battery is made and broken with 

 great rapidity. 



I have used for the long arm of the lever a piece of thick 

 sheet brass about 6 or 7 inches long and an inch broad. A 

 piece ith of an inch broad and about 4 inches long may be cut 

 out of the middle of the long arm, so that a thin plate of amalga- 

 mated copper, of platina, or of any other metal may be attached 

 to the lever by a small screw and nut, at any distance we wish 

 from the centre of motion. I have attached the amalgamated 

 copper at distances varying from 3 to 10 inches from the centre 

 of motion, and have found that it acts as well at 3 or 4 as at 10 

 inches from the centre. It is useless to make the length of the 

 long arm greater than 6 or 7 inches. I have found that the use 

 of the lever just described is a great improvement to the contact 

 breaker, not only when amalgamated copper and mercury are 

 used, but also when the contact is made by platina or any other 

 metal and mercury, or by the pressure of two solid metala 

 against each other. 



In the mercm-ial contact breaker, I have used oil, alcohol and 

 turpentine. I think the oil acts as well as either of the others, 

 and has one advantage over both of them, that it does not eva- 

 porate. The others require to be renewed every day. 



The magnetic power of the electro-magnet in the mercurial 

 contact breaker, and the shock given by the secondary current of 

 its helix, are much greater when amalgamated copper is used 

 than when platina is employed, or than when the connexion with 

 the battery is made and broken by two solid metals. Hence 

 the contact breaker I have described, in which contact is made 

 and broken by means of mercury and amalgamated copper, is 

 superior to all other contact breakers. The reason is that amal- 

 gamated copper makes better contact with mercury than platina 

 does, or than any two solid metals make with each other. 



A piece of amalgamated tin plate acts as well as amalgamated 

 copper. The part of the tin or copper which dips into the mer- 

 cury need not exceed ^th of an inch in breadth. 



The mercurial contact breaker requires much less magnetic 

 power to work it than other contact breakers ; because, in order 

 to make perfect contact between mercury and amalgamated cop« 



Fhil. May. S. 4. Vol. 15. No. 100. April 1858. S 



