xxxvi Trails. Acad. JSci. of St. Louis. 



II. Perforated disc. 



^0,2(1 — 0-2) 



^= 8E '' 



3+0- 1 



8E r 



w = - 2E ' [ 2(l + cr) (^2^ +^1') -'"'J 



^ ^ ^ pa)2(l +(7)(3 +C7) 



4E r2 



00 — ±- — ^^ — J — l^ — J I 7? 2 _L /? 2 i_ ^2 



^^ 4E [^2 -1-^1 — 7_2a'^J 



"^ 4E 7-2 * 



Professor F. E. Nipher reported that he had apparently 

 succeeded in producing a distortion of a magnetic field by 

 means of explosions. The apparatus used was a transformer 

 consisting of concentric coils wound upon brass tubes. The 

 outer tube was five inches in diameter and six feet long, wound 

 with over four thousand windings of No. 16 wire. This coil 

 was traversed by a continuous current from a storage battery. 

 Within this and separated from it by an air-space of an inch, 

 is a secondary coil of equal length having over twenty-five 

 thousand windings of No. 25 wire. This coil is connected 

 to a D'Arsonval galvanometer. Within the tube on which 

 this coil is wound is a smaller brass tube within which a train 

 of black gunpowder is laid. This tube is open at both ends, 

 and has practically no recoil when the explosion is made. 

 When hung by a bifilar suspension on cords ten feet in length, 

 the recoil is about an inch. When the exciting current is 

 small compared with the capacity of the battery, the galvano- 

 meter reading is very steady. When the train is exploded a 

 sudden and marked throw of the galvanometer results, which 



