490 Prof. J. A. Fleming. On an Instrument for the [Jan. 26,. 



in length and 8 cms. outside diameter. Over this brass tube is placed 

 an ebonite tube ee the sides of which are 5 mm. in thickness and its 

 length 80 cms. This ebonite tube fits tightly on the brass tube. The 

 brass tube is closed at the end remote from the inductance coil by a 

 plate and a pin p% which forms a bearing for the whole apparatus. 

 Over the larger ebonite tube is slipped a metal cylinder or outer jacket 

 J which can slide easily on the ebonite tube. This jacket carries a rod 



FIG. i. 



ending in a half-collar of metal K resting on the inductance spiral (see 

 fig. 2). An ebonite handle H enables the jacket to be moved to and fro. 

 It will be seen, therefore, that the arrangement constitutes a condenser 

 formed of the inner and outer brass tubes separated by an ebonite 

 dielectric, the capacity of which can be varied by moving the outer 

 jacket away from the inner. Also this condenser is in series with an 



H 



FIG. 2 . 



inductance coil, the inductance of which is reduced or increased by the 

 same movement which reduces or increases the capacity. The 

 oscillation constant of the arrangement is, therefore, variable between 

 certain limits, and its variation with the displacement of the handle H 

 follows a straight line law. 



