EECENT PROGRESS IN PHYSICS. 349 



^d of the wire a ; the upper was so near the end /9 that, in dis- 

 [harging the hattery, a small bluish spark passed. After discharging 

 jlirough the main spiral the upper plate was removed and tested by 

 he electrometer. For a positive charge of the battery the condenser 

 ijlate, which touched the end /3, was found electro-negative. The 

 Jayed figure (fig. 65) is, therefore, always produced by the end charged 

 nth negative electricity ; and, consequently, the secondary current has 

 \lways the same direction as the main current, 



' The experiment made by Riess for ascertaing the direction of the 

 ateral current by the decomposition of iodide of potassium i'ailed, as 

 |e did not succeed in producing the decomposition by the secondary 

 ^irrent.— (Pog. Ann., XLVII, 74.) 



i § 67. Defection of the magnetic needle hy frictional electricity. — The 

 ioils of a multiplier, used for producing a deflection of the magnetic 

 ;:eedle by a current of frictional electricity, must be very well insulated, 

 liess has constructed such a multiplier (Pog. Ann., XL, 348) of a 

 jopper wire 105 feet long and one-sixth line in diameter, which, 

 lovered with three coats of silk and in 260 coils, formed 5 layers on 

 -eing wound upon a suitable frame. Before winding a length of the 

 /ire it was twice covered with shellac varnish, and the wrapping 

 mt on before the varnish was perfectly dry. Each layer was again 

 larnished after wrapping. 



The cylindrical astatic needles belonging to this coil were 22 5 lines 

 png, 0.4 line in diameter, and 5 lines apart. The combined needles 

 ade one oscillation in 6.6 seconds. 



One of the wire ends of such a multiplier being placed in conducting 

 nnexion with the conductor, the other with the cushion of the elec- 

 ical machine, a deflection of 10 to 20 degrees could be maintained 

 ly turning. 

 \ \ When it is desired to deflect the needle by the discharge current of 

 ■he electrical battery the discharge of course must be retarded by the 

 iQsertion of bad conductors, such as moist strings, glass tubes filled 

 irith water, &c. 



, The latest experiments made by Riess on this point (Pog. Ann., 

 ILVII, 535) gave results showing that the deflection of a magnetic 

 ieedie by the wire which slowly discharges an electrical battery is 

 ndependent of the surface of the battery, provided a perfect discharge 

 'f the bat-tery takes place. It is therefore immaterial to the dtflec- 

 ion of the needle whether the same quantity of electricity is distri- 

 '•uted over one or over several jars. 



I Faraday had attempted [Experimented Researches, 363, Pog. Ann., 

 1:9) to compare the discharge current of the electrical battery Avith 

 ,hat of a voltaic current. After obtaining a given deflection of the 

 inagnetic needle by discharging a battery he constructed a voltaic 

 ')air, which, acting 3i seconds, produced the same deflection as the dis- 

 charge of the battery ; and he concluded that the quantity of electricity 

 'ielded by the pair was equal to that accumulated in the battery. 



Riess justly remarks, that this conclusion is not well founded, be- 

 iiause the instantaneous action of the discharge current of the battery 

 )n the needle is essentially different from that of a galvanic current. 



