Eecomhination of Ions in Air and Temperature of Air. 657 



fastened to a heavy brass rod, ???, thus forming one electrode, 

 while the other five were attached to the rod m', forming the 



second electrode. These rods were supported by the rods 

 n and ?i', which passed out through the brass tubes r and r', 

 and were supported bv the insulating ebonite plugs S and S'. 

 The brass cylinder was surrounded by a sheet-iron cylinder, 

 separated from it by a uniform air-space of about 10 cms. 

 The ends of this iron cylinder were also closed, as show^n in the 

 diagram. The cylinder and inclosed air were heated by 

 means of a long bunsen-burner which was placed underneath 

 the iron cylinder, and ran nearly the full length of the 

 cylinder. The iron cylinder was covered with sheet asbestos 

 to prevent as far as possible the heat from radiating. The 

 air between the two cylinders became heated and formed a 

 hot air-jacket round the brass cylinder, and the air inside it 

 could thus be kept at a fairly constant temperature by 

 regulating the supply of gas to the bunsen-burner. The 



