A HISTORY OF SCIENCE 



nometer, the other with a voltaic battery of ten pairs 

 of plates four inches square, with double coppers 

 and well charged ; yet not the slightest sensible 

 deflection of the galvanometer needle could be ob- 

 served. 



"A similar compound helix, consisting of six lengths 

 of copper and six of soft iron wire, was constructed. 

 The resulting iron helix contained two hundred and 

 eight feet; but whether the current from the trough 

 was passed through the copper or the iron helix, no 

 effect upon the other could be perceived at the galva- 

 nometer. 



" In these and many similar experiments no differ- 

 ence in action of any kind appeared between iron and 

 other metals. 



"Two hundred and three feet of copper wire in one 

 length were passed round a large block of wood ; other 

 two hundred and three feet of similar wire were inter- 

 posed as a spiral between the turns of the first, and 

 metallic contact everywhere prevented by twine. One 

 of these helices was connected with a galvanometer and 

 the other with a battery of a hundred pairs of plates 

 four inches square, with double coppers and well 

 charged. When the contact was made, there was a 

 sudden and very slight effect at the galvanometer, and 

 there was also a similar slight effect when the contact 

 with the battery was broken. But whilst the voltaic 

 current was continuing to pass through the one helix, 

 no galvanometrical appearances of any effect like in- 

 duction upon the other helix could be perceived, al- 

 though the active power of the battery was proved to 

 be great by its heating the whole of its own helix, and 



242 



