510 ELECTRICITY. 



Metling metals. It has before been observed that the 

 electric fluid produces no sensible effect when passing 

 through conductors. If, however, the conductor is so 

 slender that only a part of the fluid can pass upon it, the 

 rest, surrounding it, but passing through the air, gives out 

 light and heat. By this heat a narrow strip of gold or 

 silver leaf a slender, thread-like cutting of tinfoil, 

 or even a very fine wire, may be melted by passing a 

 strong charge from a battery through them. 



The degree of heat which is evolved by the passage 

 of electricity through any substance, depends upon the 

 degree of resistance which the substance opposes. The 

 more perfect the conductor the less the heat. If the me- 

 tal is one of those which are the most perfect conductors, 

 it will require a larger charge to produce a sensible ef- 

 fect in warming it. Wood is a very imperfect conduc- 

 tor, consequently a small quantity of electricity will 

 affect its temperature, and a piece of considerable thick- 

 ness may be warmed by repeated discharges. 



In consequence of this fact, that the conducting power 

 of the metal upon which the experiment is tried, influ- 

 ences very much the degree of heat evolved by the trans- 

 mission of electricity through it, some philosophers have 

 endeavored to ascertain the different conducting powers 

 of the metals, by observing the comparative difficulty 

 with which they are melted by electricity. The experi- 

 ments may be performed in the following way. 



Connect with the outside coating of a battery, which, 

 in order to secure the success of the experiment, should 

 contain at least thirty square feet of coated surface, a 

 wire of one fiftieth of an inch in diameter, and two feet 

 long. With a smaller batteryf the experiment will suc- 

 ceed, if the experimenter is satisfied with a shorter or 

 slenderer wire. The other end of the wire must be fas- 

 tened to the end of a discharging rod. When the bat- 

 tery is fully charged, the ball of the discharger may be 

 brought into connexion with the knob communicating 

 with the outside of the battery, and thus the whole charge 

 will be sent through the wire, which will be made red 

 hot through its whole extent, and even melted so as to 

 fall in glowing pieces to the floor. ' When a wire 



