Air suhjected to X-ray 's, 537 



copper tube from the rest of the apparatus, not only with the 

 paraffin, but also with a glass tube of 30 to 40 centimetres in 

 length, to lessen the discharge of the tube of copper, as 

 happens through convection, by means of the same active air. 

 Filters made with brass tubes (10 x 2*5 centimetres) closed 

 with 30 to 60 disks of strong gauze of brass, copper, or alu- 

 minium, when traversed by a current of active air, take a 

 positive charge to a potential of 15 volts, increasing a little 

 with the number of the disks, and perhaps with the fineness 

 of the meshes of the gauze adopted. 



Square pieces of not very fine gauze of brass, 20 to 25 or 

 more centimetres in the side, rolled and wrapped round 

 themselves, and introduced, into suitable tubes of glass or of 

 metal, take positive charges from 15 to 20 volts when they 

 are traversed by a current of active air. 



Some metallic leaves equal in size to the pieces of gauze^ 

 and rolled up in a similar manner, all took from the current 

 of active air negative charges with a potential of about 

 10 volts. The experiments were made with leaves of copper, 

 iron, zinc, brass, tinned iron, platinum, aluminium, and tin. 

 The charges varied principally with the way in which the 

 leaves were rolled up. 



Strips of the metals mentioned, 51 centimetres long by 

 2*7 centimetres broad, introduced into a tube of glass or 

 metal and subjected to streams of active air, charged them- 

 selves at least to a potential of 3 to 5 or more volts. The 

 strip of polished aluminium often took a lesser charge than 

 the others. The strips of gauze equal in size to those of 

 sheet metal took negative charges, similar, but sensibly 

 superior to those assumed by the sheet metal strips. 



Finally, the closed tubes and the brass wires introduced 

 into tubes of glass or metal charged themselves negatively 

 when they were subjected to streams of active air. 



It seems that the metals, independently of their nature, 

 take a positive or a negative charge according to whether 

 the active air rubs against them with force or lightly ; and 

 this result is confirmed by the following experiments. 



Tubes of copper or of lead, if short, and particularly if 

 straight, traversed by active air take a negative charge; but 

 if long, and particularly if coiled upon themselves, take 

 positive charges which may attain sufficiently high potentials. 

 Coarse turnings of copper well rammed into a tube of 

 glass or metal take a positive charge from active air ; but if 

 inserted in small quantity and sparsely, they take a negative 

 charge. 



Cylinders of diverse sizes, made with leaves of gauze of a 

 Phil. Mag. S. 6. Vol. 1. No. 5. May 1901, 2 N 



