THE MEASUREMENT OF RESISTANCE 213 



Evershed "Megger." It is highly desirable to have some 

 convenient portable instrument for measuring insulation re- 

 sistance, which shall be rugged in construction, direct reading, 

 capable of giving results with rapidity and so simple in manipu- 

 lation that it may be employed by persons not accustomed to 

 the use of delicate instruments. In addition, the device must be 

 capable of furnishing a testing voltage so high that it will search 

 out defects of high resistance. 



FK.. 121. Everahed 



The Evershed Megger, Fig. 121, was designed with these require- 

 ments in view. 



Referring to the scheme of connections, M and M are permanent 

 magnets which furnish the fields both for the instrument proper 

 and for the small hand-driven magneto Z>, which gives the testing 

 voltage. The movable element consists of the coils BB' and 

 A which are rigidly connected; flexible leads are taken to the 

 coils but there are no controlling springs. 



