332 



[Dec. 18, 



the glass bulb was broken. This tube consequently contains vapour 

 of iodine. 



No. 319 (Plate I.) is 20 inches long, 4 inches diameter: one ter- 

 minal consists of aluminium, cup-shaped, about 3 inches diameter ; the 

 other a wire of the same metal. There is about 14^ inches between 

 the cup and the wire. 



No. 320 is 3 inches long, 1 inch diameter : very thin platinum 

 wires, f ths of an inch in length from the part protected by glass 

 tube, are placed 1 J inch apart from point to point in the tube. 



No. 315 and No. 324 (Plates I. and II.) are about 5 inches long, 

 with two balls of aluminium f ths of an inch diameter, and 3 inches 

 apart : the balls are attached to platinum wires, these wires being also, 

 as in No. 248, hermetically sealed and protected with glass tubing. 



The vacuum in each of the tubes was obtained by the carbonic 

 acid process. 



10. Fig. 1 represents the general arrangement of the apparatus : 

 A, B, C, the three batteries (5); z and c the zinc and copper ter- 

 minals of each battery ; the discharge of 1 1 20 pairs, of 2240, or of 

 3360 can be thus separately examined. My general practice is to 

 place the experimental tube between either one or the other of the 

 batteries (fig. 2), the negative or zinc terminal of C being attached 

 to one wire, and the copper or positive of B to the other. A and B 

 are then connected, and the circuit is completed either by a resistance 

 arrangement being attached to the zinc terminal of A and the copper 

 terminal of C, or the circuit is closed by a wire. It was with the 

 view of being enabled to vary the resistance at pleasure, that I 



