314 



may be usetl in the circuit in series to increase the resistance. Fig. 10 

 gives a view of a median vertical longitudinal section of the slide. It con- 

 sists simply of a thick glass slide A, on which is a heavy layer of tin-foil 

 B B\ and on this a plate of copper C C\ through which the binding posts 

 G and H are screwed. This not only fastens B B^ and C together, but 

 fastens them to the glass slide A. The specimen is laid at L with its 

 ends touching the ends of the tin-foil B B\ on which the cover glass rests 

 at 00\ 



