Charged Bodies at Moderate Temperatures. 445 



The experiment was varied by placing the zinc strips on the 

 "bottom and on the shelf of the iron box, no new supplies 

 of salt or of iodine being added. The zinc was thus in 

 metallic connexion with the case of the electrometer, while 

 the insulated terminal was connected to the iron plates, now 

 ■with nothing on. 



It was found that the iron plates differed in potential 

 from the surrounding box by about *5 or *6 of a volt 

 positive. A charge given to the plates leaked away till this 

 steady reading was reached. 



It was found that no change in this potential-difference was 

 produced by varying the distance between the zinc and the 

 insulated iron. 



Experiments of an exactly similar nature were made with 

 bromine substituted for iodine. The results obtained were the 

 same. The difference of potential was not, as a rule, the same 

 in any two experiments on different days even with the same 

 materials. This is not to be wondered at, as the iron box and 

 the plates were thoroughly cleaned after each experiment, and 

 a different surface state produced each time. 



Common salt was next sprinkled over a copper plate and 

 iodine sprinkled on it ; this was insulated in a zinc box : it 

 was found that after heating for half an hour there was a 

 slightly increased leak of positive electricity and practically 

 no increased leak of negative electricity. On the other hand, 

 when the salt was placed on the bottom of the zinc box and 

 iodine sprinkled over it, there was a greatly increased leak of 

 electricity from the insulated copper plate when it was 

 charged negatively, and practically no increased leak when 

 it was charged positively. It was also found that the 

 steady reading showed the copper to be positive to the zinc 

 box. 



§ 1 0. The following results are given to show roughly the 

 nature of the effects observed. The insulated plate in the box 

 was supported as described in § 2. It was connected to the 

 insulated terminal of the quadrant-electrometer ; the sur- 

 rounding box was joined to the case. 



The insulation was first tested without flame and found 

 good. The insulation was also good with flame and with 

 nothing on the insulated iron plates. 



