380 



Electro-Magnetic Experiments 



A convenient apparatus for this dig- 

 ital experiment consists of two copper 

 wires coiled at one end into a close 

 flat spiral C and bent at the other end 

 P at right angles downward. The 

 coils being placed flat on the table 

 with the disc of antimony A between 

 them and the bent ends in the mercury cups of the galvanometer, the 

 apparatus is ready for experiment. 



4. With one fourth of a grain of antimony between two straight 

 wires the needle was deflected 22° upon the application of the fin- 

 gers. 



5. A piece of copper wire one sixteenth of an inch in diameter 

 and 2 inches long being laid with its ends across the copper wires 

 (the poles or termination of the coil of the instrument) and one of 

 the junctures pressed between the thumb and finger the needle was 

 deflected 6 degrees. 



I have constructed an electro-magnetic multiplier upon the plan 

 of Schweigger with 120 coils within one inch of the needle above 

 and below it. It is affected by water ; but not by the thermo-elec- 

 tricity produced by animal heat. 



I have also constructed a dip- 

 ping ring. It is a coil of about 

 40 turns in a circle of 5£ inches 

 in diameter. The ends of this 

 coil terminate in two brass pivots 

 diametrically opposite to each 

 other. These pivots which are 

 small, roll on two horizontal 

 straight edges and have their ex- 

 treme ends, which are amalga- 

 mated running in mercury con- 

 tained in little copper troughs. The mercury rises, by its tendency 

 to form a globule, above the trough which contains it, thus uniting 

 itself to the pivot which is straight. The ring being nicely balanced 

 like a dip needle, and a current of electricity sent through it, by 

 bringing the poles of the galvanometer into the mercury troughs, 

 will turn on the pivots till its plane is perpendicular to the axis of the 

 true dip of the place. It is difficult to make the pivots so true that 

 the ring will turn at once into the plane unless we go to the expense 



