198 



ELEMENTS OF GENERAL SCIENCE 



"safety valve" in the electric circuit. This fuse wire is made 

 and labeled in various sizes so as to limit the strength of 

 the current to any selected value. Such a fuse is often to 

 be found near the electric meters in a building, and may 

 be observed but should not be disturbed. 



COPPER BLADE 



PORCELAIN 

 *- SCREW CONTACT 

 FUSE WIRE 



FIBER TUBE > 

 INDICATOR WIRE 

 FUSE 



FILLING 



of fuses 



A-C, simple fuses designed to hook over connecting posts ; D, an ordinary screw- 

 plug fuse ; E-H, fuses to be slipped into fuse openings so that the fuse ends connect 

 with electric wires 



The open-link fuse (fig. 97, A, B, C) is unreliable and often 

 unsatisfactory because little drops of molten metal deface the 

 supporting board and may injure the operator. Another type 

 of fuse contains a metal wire or strip which can be renewed, 

 but this is covered with a tube of fiber (fig. 97, ). Other 

 fuses are filled with a material which does not catch fire when 

 the fuse burns out or explodes (fig. 97, 2?, F). Telephones 



