290 



A. TANAKADATE 



take the place of circular coil« when absolute determinations of electro- 

 magnetic constants are required. One such instrument is represented 

 in Fig. 8. It is essentially the same as an old form of current 



Fig. 8, 



detectors, constructed however with due regard to the proportional 

 dimensions which theory shows to be best. 



The following calculation of the proper distance between two 

 rectangular coils is made not so much for the sake of the flat coil 

 galvanometer as for the sake of the internal coil mentioned above 

 (page 279) and described in detail below (page 296). 



Let 2a be the distance beijsveen the two coils, 

 ,, 2b ,, ,, height of the coils 

 „ 2c „ „ length „ „ „ . 



Let X, ij, z be the co-ordinates of any point referred to the centre 

 of the coils as origin, axes being parallel to a, 5, c. 



