Instruments and Experiments. 105 



tremity of the helix, pass down through the base-board, under- 

 neath which they are soldered to the cup c. The similar ends 

 at the other extremity of the helix, likewise pass down through 

 the base-board, underneath which they are connected with the 

 middle brass band e, which is surmounted with a brass cup con- 

 taining mercury. Into this cup descends a copper wire 5, con- 

 nected above with the wire w^ w, which by means of clock-work 

 set in motion by a concealed spring, wound up at the milled head 

 d, is made to vibrate rapidly, and to dip alternately into glass 

 cups for containing mercury. The glass cups are open at bot- 

 tom, so as to allow the mercury to be in contact with the brass 

 supports, into which they are cemented, and which are fastened 

 to the outer brass bands b and b\ These brass bands are con- 

 nected underneath the base-board with a cup &, not seen in the 

 figure and corresponding to c. Both the cups c and c', are fur- 

 nished with binding screws to confine the wires by which the 

 inner helix is connected with the battery. 



Exterior to the helix just described, enclosing it and insulated 

 from it, is another composed of about two thousand feet of small 

 insulated wire, the two extremities of which are soldered to the 

 cups ni and w/, likewise furnished with binding screws. H and 

 H' are handles for shocks, connected with the cups m and ni'. If 

 we now suppose the copper pole of a voltaic battery to be con- 

 nected with the cup c, and the zinc pole with the corresponding 

 cup c', the battery current will circnlate unbroken through the 

 several strands of wire composing the inner helix, to one of the 

 outer bands; thence by the vibrating wire to the middle band, 

 and thence to the cup &, whenever either end of the vibrating 

 wire dips into the mercury of the glass cups. As the vibrating 

 wire approaches to a horizontal position, previously to the other 

 end's dipping into the mercury of the other glass cup, the battery 

 current is broken, and a bright spark is seen in the cup, in which 

 the ruptare of the current has just taken place. If the handles 

 be grasped with moistened hands, severe shocks will be felt. 

 Introduce into the helix a brass tube, and the spark becomes 

 quite small, and the shock feeble. Next introduce a bundle of 

 soft iron wires into the brass tube, and the spark and shock are 

 not sensibly increased. If the tube be now withdrawn from 

 the helix without withdrawing the iron wires, the spark will be- 

 come exceedingly brilliant, and the shocks so severe that they 



Vol. XL, No. 1.— Oct.-Dec. 1840. 14 



