of High Specific Resistances. 463 



A made 25 vibrations in 125 seconds. 

 B „ „ 124 „ 



C „ „ 105 „ 



After remagnetizing the magnets with about half as much 

 current again round the electromagnet, it was found that 



A made 25 vibrations in 123 seconds. 

 B „ „ 107 „ 



C „ „ 107 „ 



B therefore was improved ; A and C remaining about the 

 same. The deviations were probably produced by the un- 

 avoidable shaking and jarring in mounting the magnets, 

 though this was done with considerable care. 



These magnets were next observed with respect to their 

 behaviour with one of the coils. Coil u No. 3 " was selected 

 for this purpose. It was placed on the table, and above it 

 hung a specially fine spring- coil of wire forming part of a 

 Jolly's balance. The magnets were hung from the end of 

 this spring by a loop of silk, and could be adjusted to pene- 

 trate the coil to a greater or less extent. In general five 

 positions were taken : — 



Position 1. Magnet-end flush with the upper windings of 

 the coil. 

 „ 2. Magnet-end at \ of the length of the hole 



through the coil. 

 „ 3. Magnet-end at the centre of the coil. 

 „ 4. Magnet-end at f of the length of the hole 



through the coil. 

 „ 5. Magnet-end flush with the bottom of the coil. 



Three Leclanche cells were allowed to run for four hours 

 through the coil before the experiment began. The coil had 

 a resistance of 3130 ohms. 



First, a series of observations was taken by observing on 

 the glass scale the equilibrium position of the magnet with 

 the current direct and reversed. The magnet was then 

 lowered to position 2, and so on ; then it was reversed and 

 the experiments repeated. Two complete sets each way were 

 made for each magnet, i. e. forty observations of distance and 

 forty reversals of current. The experiment was a very pretty 

 one, and I never remember to have seen any apparatus work 

 better. The following set is given as a sample from the note- 

 book. The numbers, of course, have no significance except 

 with respect to the actual coil and magnet taken. 



2 M 2 



