78 ELEMENTS OF LABORATORY WORK 



body in a new system. In other words, this inductive action 

 may affect a large number of bodies placed at increasing 

 distances from the inducing body, the action diminishing with 

 the distance. It may also be noted that the action depends 

 solely on the linear distance, and not at all on the direction, 

 provided that other bodies be not introduced into the field. 



Additional Exercises and Questions. 



1. Show that two mutually electrified bodies behave, when separated, 

 as if they were joined by some extensible but elastic material. 



2. Under what conditions may the electrification of a given body be 

 communicated to a non-conducting body ? 



3. In the electroscope and electrometer, the bodies between which 

 mutual changes are taking place are shielded or screened either by wire- 

 work or tinfoil. Give reasons for this in each case, and point out any 

 difference in their application to the two kinds of instruments. 



4. Make experiments with a view to discovering the amount of 

 electric change which can be produced within a hollow metallic body 

 by means of an electrified body held outside. For this purpose intro- 

 duce any instrument or system, which is sensitive to electric changes, 

 within a wire cage or any hollow metallic vessel. Compare results both 

 with and without contact between the body inside and the cage, and 

 also when the hollow vessel is in itself strongly electrified. 



5. Place a sensitive electroscope in metallic contact with a hollow 

 vessel, and observe the effect of placing within the vessel a ' charged 

 body,' and also of putting it in contact with the vessel from the 

 inside. 



6. From your observations of electrificat ion what suggestion can you 

 make as to their origin ? 



7. What experiments demonstrate that the origin of electric changes 

 lies in the condition of tke space around those bodies which manifest 

 the changes, that this condition will vary with the nature of the sub- 

 stan^es also occupying- the space in question, but that space which is 

 filled by conducting matter cannot exhibit the properties of which it is 

 otherwise capable ? 



8. Show that conducting matter may become electrified by friction 

 if it is insulated. Place a metallic plate upon a sheet of ebonite or 

 paraffin ; connect the plate with an electroscope at a convenient dis- 

 tance, and rub it with a piece of fur. The electrophorus may be 

 utilised for the purpose, but take care that the cake of ebonite itself 

 is not electrified. Passing through a flame will discharge it. 



