ELK.MLMAKY LAWS uF CUNTINUHJS CURRENTS 5 



permit the passage of an electric current as conductors. 

 If the two terminal- of an electric generator, or those of a 

 primary cell, are connected by a piece of dry string, or a 

 stick of dry wood, it will be found that no current passes 

 through the connecting piece of string or wood; such bodies 

 a> these are called insulators. On the other hand, if the two 

 terminal- are connected by any metallic body, or by a piece 

 of carbon, current will flow from the terminal of higher 

 electric preure to tin- om- >f lower electric pressure and 

 such bodie- arc called conductors. 



/.' Now if we make up a set of connecting 



-of various materials wit 1- which to join the terminals 

 of the generator and have -<>me means of measuring the 

 amount of current that Hows between the generator ter- 

 minals when the different connecting -trip- are u-ed. it will 

 be found that the current which flows will vary with the 

 different connectors. Although the e.m.f. of the generator 

 is the same 1 when the variou< connect. used a heavy 



current will How through some of them, a smaller current 

 through others, and an imperceptible current through 

 others. From thi- experimentally observed fact we get the 

 idea of resistance; apparently x<n< <>f (luxe connecting strips 

 offer more resistance to ///< passage of an electric current 

 than others. 



Conductors uml Inhibitors. The difference between a 

 conductor ami an insulator cannot be sharply defined, 

 because no body i- a perfect conductor (one having no 

 resistance and no body is a perfect insulator (one having 

 infinite resistance). This point must be kept in mind; 

 for empha-is we will illustrate it by an example. If we 

 make up a set of strips of various substances, all of the 

 strips being of equal cross-section and length, then use 

 them to connect the terminals of a generator and measure 

 the amount of current that flows through each we might 

 get results as shown by the table, page 6. 



