332 



TENTH ANNUAL REPORT OP 



/r7% 



For inserting wires conveniently into the circuit, a binding 

 screw, such as represented in Fig. 6, may he used. No ex- 

 tended explanation of its application is needed. Fig. 7. 



For fastening thick wires in the holes of the binding 

 screw, they should he at least one line in diameter. But 

 the retaining of these wires is thus rendered some- 

 what difficult, and in frequent use there is danger 

 in squeezing off their ends. Since the insertion wire 

 must not be too thick, and should always have the 

 same length, it is well to solder the ends of the wire. to a piece 

 of copper or brass about 2.5 millimetres thick, which can be 

 easily fastened in the holes of the clamp. 



Norrenburg used for metallic connexion of pieces of wire, 

 Fig- 8. wire-feathers (Drahtfe- ^'s- 9- 



dern)suchas represented 

 in Fig. 9. These wire- 

 feathers are to be recom- 

 mended because connect- 

 and separating, by 

 means of them, can be 

 done very easily and 

 rapidly. 



It is very evident that 

 for insertions, wire of 

 different lengths can be applied advantage- 

 ously to a rheostat. 



Denote by E the electro-motive force of the 

 galvanic battery, by R the essential resistance to conduction ; then Ave 

 have, according to Ohm's law, the force of the current, 



E 



P 





\U 



(1) 



with perfect metallic closing — that is, with such closing.that its resist- 

 ance to conduction, compared with that of the elements, may be dis- 

 regarded. Introducing the reduced length of wire I, tlie force will be 

 only 



We have here s and s' given by observation ; I is also known, and 

 from these two equations E can be eliminated, and the value of R com- 

 puted. The following tables give a series of observations instituted 

 for determining the resistance to conduction of different batteries : 



