528 BELL SYSTEM TECI I XIC.ll. JOl'RSAL 



telephonic frf(|iR'nries without the iiecessitN' ot winding magnetizing 

 coils upon then). The maximum temperature at which measure- 

 ments can lie nuuie with this apparatus is about 1,000° C. By tilling 

 the unhealed fuinace with liquid air, a minimum temperature of 

 — 190° C is attainable niakini; the whole range of the instrument 

 about 1,200° C. 



The changes introduced in order to adapt to pernieameter for 

 measurements at different temperatures do not impair its accuracy, 

 the determination of permeability at both high and low temperature 

 ha\in^' the same precision as at room temperature. 



