Protective or Circuit Breaking Device. 



277 



mounted as shown in figure 4. See also fig. 6 for an end view. 

 Corresponding letters are used in figures 3, 4, and 6. K, L, 

 M, and N, fig. 4, are 4 glass discs blown on the small tube 

 G"H" which is contained in the larger exhausted tube GH. 

 The discs are 3'8 c ' ras in diameter. The distance from K to L is 

 lT-S"" 8 ; from L to M l-27 cms ; and from M to N 17'8 cms . The 

 whole length of the tube is 5O8 0ms . The four arms in DC, figure 

 3, are strung on the discs M and N, figure 4, as shown by 

 the dotted lines. Each arm taking up six lengths, has its 

 terminals at JS". An end view of the disc with the binding 

 posts for these terminals is shown in figure 6. The brass 

 binding posts E, R, etc. are fastened to a plate of mica which 

 is cemented to the disc. 



Fig. 5. 



i' it 



Small glass hooks fused to the edge of the disc support 

 the wires. In fig. 6 it may be seen how one wire or arm is 

 mounted. One end is permanently fastened to C and the wire 

 stretched for six lengths from disc to disc and also permanently 

 fastened to E. The loop between E and R is a continuation 

 of the wire and is used for adjusting it equal to the one next 

 to it. One arm, then, is included between C and R ; another 

 one between R and D, and so on. The other end of the tube 

 is similar to this, with the exception of not having any leads, 

 such as AA', fig. 6, fused into the glass for heating the bridge 

 EF. With the bridges EF and DC, fig. 3, mounted as shown 

 in fig. 4, and the tube GH exhausted very nearly to a Crookes 

 vacuum, radiation was the only controlling factor for the heat 

 in EF and DC. A storage cell with a resistance in series was 

 used to furnish the bridge current. 



