of Edinburgh, Session 1883-84. 
415 
lead or bismuth to become positive. Hard rubbing was doubtless 
the cause of his anomalies also. 
The method by metallic powder was employed by Singer* and 
Becquerel. The former experimenter allowed the powder to fall 
through a sieve of haircloth, flannel, or muslin. He found the 
powder always negative, whether it was of copper, iron, zinc, tin, 
bismuth, antimony, nickel, or graphite. Here the friction was 
gentle, and in consequence no anomaly. Becquerelf experimented 
with filings of copper and of zinc. He allowed the filings to fall 
on a slant plate (in connection with the earth), and to drop into a 
metallic receiver attached to the knob of an electroscope. He found 
that the copper filings were positive, when the plate was of 
Copper, zinc, lead, tin, iron, bismuth, antimon}^ ; 
and without any sensible charge when the plate was of 
Platinum, gold, silver. 
With zinc filings, the following were negative — 
Platinum, gold, silver, copper, graphite ; 
and the following positive— 
Zinc, iron, bismuth, antimony. 
These results, so far as they go, agree very well with those I have 
obtained, and that agreement proves that the metals may be com- 
pared by rubbing them all with one suitable substance. 
Hone of the investigators mentioned place the metals in a scale ; 
Becquereks results place them in three groups. The only scale 
which I have found published is a qualitative one by Gaugain. 
He experimented with discs of about 7 cm. diameter, formed of 
gutta percha, and gutta percha rubbed for a greater or less time 
with sulphur. He rubbed such an insulating disc with wires of the 
different metals ; and the place of the metal was determined by the 
kind of electricity produced and retained on the disc. The scale or 
rather classification is as follows — 
Aluminium — 
Gutta percha. Ho. 1. 
Elem. de Elekt., 1819, 199. + Ann de Chim. et de Phys., 47, 116. 
