The History of Electrical Resonance

T h e L e y d e n jar, discovered in 1746, was for m a n y y e a r s one of t h e most i m p o r t a n t i n s t r u m e n t s in the meager e q u i p m e n t of electrical experimenters. W h e n the j a r was charged b y a n electrical m a c h i n e a n d t h e discharging k n o b s b r o u g h t close enough t o g e t h e r a s p a r k would j u m p between t h e m . T h e s a v a n t s of those d a y s reasoned t h a t this d o u b l y c o a t e d jar was a storer of electricity, a condenser; t h a t before t h e s p a r k passed there was an accum u l a t i o n of positive charge on one coating a n d of negative on t h e o t h e r ; a n d w h e n t h e s p a r k passed these charges neutralized each o t h e r a n d the j a r was discharged. B u t t h e y did not know or suspect t h a t this discharge was oscillatory, t h a t first one side a n d t h e n the o t h e r b e c a m e positively charged, until t h e motion g r a d u a l l y c a m e to rest. T h e view t h a t such was the case seems first to h a v e been p u t f o r w a r d in 1826 by Felix S a v a r y , in F r a n c e . It h a d been observed by him, a n d v e r y likely by others as well, t h a t a steel needle m a g n e t i z e d by the discharge of a L e y d e n jar did not in all c i r c u m s t a n c e s h a v e the s a m e polarity. In t h e following words he suggested the idea t h a t the results were clue to t h e oscillatory discharge of the j a r : " A n electric discharge is a p h e n o m e n o n of m o v e m e n t .