20 Mr Zeleny, On Convection Currents and on the [Oct. 31, 



One of these is represented by P, the other one being parallel 

 to it, and both being supported by rods (not shown) which were 

 fixed at right angles to them. 



The plates were kept at a constant difference of potential by 

 a battery of cells, and were completely surrounded by a lead box 

 BB' . The potential of points between the plates was investigated, 

 during conduction, by means of a fine brass wire W, -^ of a milli- 

 metre in diameter, which was supported by a frame F. This 

 frame was fastened to a microscope stand 8, which allowed by 

 means of the set screws T and JJ of two motions at right angles 

 to each other. The position of the wire was determined by means 

 of a verniered scale at V. 



The parts of the wire not included between the plates were 

 surrounded by the brass guard-tubes H and J which tapered to a 

 small size at their ends. 



The wire was stretched taut between two small insulating rods 

 which were carried by the parts Z and Z'. 



It was connected by means of the wire E with the gold-leaf 

 G which, supported by the paraffin block R, hung in a box of 

 which C and C' formed two sides, the other two being of glass. 



Parallel to the gold-leaf was the adjustable brass plate D 

 which was connected to earth through a high resistance by the 

 wire Q. 



The lead cover Y served as a screen for a part of the appa- 

 ratus. Earth connected metal screens also covered the exposed 

 sides, but are not shown in the figure, nor is the microscope by 

 means of which the movements of the gold-leaf were observed, 

 and which carried in the focus of its eye-piece a finely divided 

 scale. 



V*"*" 8 "" - *-^ 



Fig. 3. 



The electrical connections can be seen better from fig. 3 where 

 the apparatus is viewed from above, and where the letters have 

 the same significance as in fig. 2. 



