196 



ELEMENTS OF GENERAL SCIENCE 



light are consumed and cease to be useful as light producers. 

 There are very few materials which will endure heating to 

 the white heat which is observed in the best electric lamps. 

 Tungsten and a few other metals may be so heated, but 

 even in the best tungsten lamps the amount of light given 

 off represents about 4 per cent of the energy used in the 

 lamp ; the remaining 96 per cent is given off as heat. 



FIG. 96. Apparatus for study of an electric circuit 



The handmade mounting board with porcelain cleats, binding posts with screws, 

 and switch provides a simple and effective means of studying electricity. The 

 electric generator consists of three dry cells connected by insulated copper wire. 

 At the right, above, is a loop of small wire fastened to the binding posts so that 

 the heating effect of electricity may be studied ; at the right, below, are four 

 spools of wire of different sizes for use in the same experiment 



Is the heating and lighting effect peculiar to the wire in 

 a lamp or can it be produced in any wire ? To answer this 

 question we must learn something about the materials to be 

 used, most of which can be purchased at an ordinary hard- 

 ware store. In figure 96 some of these materials are arranged 

 so as to make a complete path for the electric current. When 

 all the wires are properly connected (the covering or insu- 

 lation must be removed to secure good metallic contact), as 

 shown in the figure, a loop of wire fastened to the upper 



