Intelligence and Miscellaneous Articles. 475 



If the wire is infinitely long, then (if, for z=0, <p= cos nt) is 

 0=e-/3* cos (nt — otz). 



Further, the following case is discussed : — that the wire possesses 

 the length I, but has its termination connected with one of the 

 coatings of a condenser, the other side of which is led away to 

 earth. For the calculation in question, as well as the rest of the 

 working, which cannot well be given in abstract, we must refer the 

 reader to the original memoir. — Beibldtter zu den Anncden der 

 PhgsiJc und Chemie, 1878, No. 1, vol. ii. pp. 221-223, 



EXPERIMENT FOR ILLUSTRATING THE TERRESTRIAL ELECTRICAL 

 CURRENTS. BY PROFESSOR WM. LEROY BROUN. 



The following experiment enables a lecturer to exhibit to a large 

 audience, in a very simple way, the action of the currents of elec- 

 tricity that pass around the earth. The experiment was suggested 

 on reading an article by Professor J. W. Mallet, in the Philoso- 

 phical Magazine for November 1877. 



A rectangular frame was made of light poplar wood, of section 

 three by two centimetres, whose sides were in length a fraction 

 over a metre, and in breadth three fourths of a metre. About the 

 perimetre of this rectangular frame were wrapped twenty coils of 

 insulated copper wire ; each extremity of the wire was made to 

 terminate near the centre of one of the shorter sides, and passing 

 through the wooden frame was fastened and cut off about three 

 centimetres from the frame. This rectangular frame was then so 

 suspended, in a horizontal position, by wires attached to the frame 

 of an ordinary hydrostatic balance, that the longer sides were at 

 right angles with the beam. By adjusting weights in the pans the 

 index of the balance was brought to the zero-point. Two small 

 orifices bored in a block of wood, a centimetre apart, served as 

 mercury-cups, in which the extremities of the short terminal wires 

 were immersed. Near the bottom and through the walls of these 

 wooden cups were screwed small brass hooks, which served as 

 connexions, to which the wires of the battery were attached. The 

 balance was now so placed that the longer sides of the suspended 

 rectangle were at right angles with the magnetic meridian or in the 

 magnetic east-and-west line. 



"When the current from the battery was made to pass around the 

 rectangle from east to west on the northern side, and from west to 

 east on the southern side, by the theory of terrestrial magnetism 

 the northern side of the rectangle would be attracted and the 

 southern side repelled; and that this was so, the corresponding de- 

 flection of the balance rendered plainly visible. When the current 

 was reversed the deflection was in the opposite direction. By 

 breaking and closing the circuit at proper intervals to augment the 

 oscillations, the large frame was readily made to oscillate through 

 an arc of five degrees. When the sides of the rectangle were 

 placed north-east and south-west the current produced no sensible 



