txEctmcity. 169 



etren of the smoke, and its colaur change so regularly, ^, 

 that we may call it a coloured portrait of the oscillatory metals explo- 

 expansion of electricity. From the* Constant recurrence *^ed by large 

 of the phenomenon, it is evident that this appearance is 

 Hot an accidental etfect, for let the experiment be made 

 with any metal, the result will be similar without excep* 

 tion. Van Marum has in numerous and faithful repre- 

 sentations explained this experiment, which may save us 

 the trouble of repetition.. The regularity of this image 

 may be seen by another method. If electricity acted on 

 the metallic thread by an expansive force solely, all the 

 Clauds of the vapaur would be parraUel and straight : but 

 as each conductor acts with a repulsive force on the near- 

 est extremity of the thread, the clouds of vapour thrown Van Marujn*$ 

 to the two extremities by two powers w^hich cross each experimente. 

 other perpendicularly, follow the diagonal of those powers 

 or rather, as the powers are constant and unequal, the 

 clouds represent the ^ image of a curved line, whose con- 

 cavity is opposed to the metallic thread. The more dis- 

 tant a cloud is from one of the conductors, the less will it - 

 be affected by the repulsive force parallel to the thread, 

 and the nearer will its position approach to the perpendi- 

 cular force of the wire. 



In the middle of the wire exists a perfect equilibrium 

 of the opposing powers ; and consequently the position of 

 the shade will be exactly perpendicular to the wire. 



The foregoing appearances will not be obtained if the 

 force employed to evaporate it be too strong ; l^ut even 

 in this case the figure will describe a zigzag, at each sec- 

 tion of which, indications of the above order may be dis* 

 cerned. 



An examination of the dectric spark will afford us The electric 

 another proof. If the conductors, between which the '?^f^. ^^^^^ 

 spark appears, be pretty close, the spark is differently 

 coloured at its two extremities, being red on one gide an^ 

 blue on the other, whilst the centre is white ; but if the 

 conductors be placed further apart, the spark will vary 

 its colour as often as it makes transitions from positive to 

 negative. 



All that has been here observed of electricity is equally Undulation or 

 applicable to magnetism. The action of the load-stone f?^^.^ observa- 



VoL. XV,— Oct. 1806. Z originates tism!^ "^*sn«' 



