Protective or Circuit Breaking Device. 



275 



A piece of chromate similar to the one under test was 

 prepared, and a current with considerable density was passed 

 through it for about 18 hours. No trace of transformation or 

 decomposition could be found. Time did not permit any- 

 further investigation of the causes for the unstable condi- 

 tion of the chromate at these temperatures, and since this 

 behavior did not warrant its use for a protective device, the 

 principle of the Nernst lamp was abandoned for the time 

 being. The chromate will be examined again in the near future 

 with the hope of obtaining more definite data. 



The original problem was now attacked on the principle of 

 the bolometer. Figure 3 shows the general plan of the appa- 



Fig. 3. 



B, 



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I 



V 



ratus. B 2 is the battery furnishing the bridge current. IV 

 and VG' are two resistances of about 10 ohms each adjusted 

 very nearly equal. The eight arms in the bridges EF and DC 

 were adjusted electrically equal as nearly as possible. Each 

 arm consisted of about 10 ohms resistance. The bridge, then, 

 as a whole, balanced for a wide range of current, and remained 

 so for any variation of room temperature. B; is the source 

 used to heat the small bridge DC, thereby unbalancing the 

 large bridge, and consequently having a current through R. 

 JR. is a relay which contains in its circuit a tripping magnet. 

 If then the source B, were shunted off the line, and the line 



