of Eclmhurgli, Session 1883-84. 
413 
number of points which come together is increased by sliding the 
one substance over the other. But whether friction is a form of 
contact, or contact a form of friction, or the two co-ordinate to one 
another, it is interesting to inquire whether the metals can be 
arranged in an electro-frictional series similar to the electro-contact 
series ; and if so, to observe the relation of the former to the latter. 
What is the present state of our knowledge on this subject ? 
Experimenters have used one or other of two methods, either rub- 
bing the metal with an insulating substance, or brushing it with a 
metallic powder. Observations cannot be made, or at least have 
not as yet been made with success, by rubbing two metals directly 
against one another, as their high conductivity allows the generated 
electricities to combine too quickly. Information on this subject is 
contained in the treatises of Reiss and Mascart. 
Haiiy,* rubbing with a woollen cloth, found that the following 
metals became positively electrified — 
Silver, lead, copper, zinc, brass, bismuth ; 
while the following became negatively electrified — 
Platinum, palladium, gold, nickel, iron, tin, arsenic, antimony. 
Faraday,! oii contrary, using the same material for a rubber, 
found that silver and copper became negatively electrified. When 
these two are taken out of the former list, the four left — lead, zinc, 
brass, bismuth — are metals which are easily disintegrated ; and that 
we shall find is the reason why they become electrified in the oppo- 
site manner from the others. 
Dessaignes,! also rubbing with a woollen stuff, gives a wholly 
indefinite result, — that gold, platinum, silver, copper, iron, bismuth, 
zinc, tin, antimony, lead, are sometimes positive, sometimes nega- 
tive, and sometimes neutral. He considered that the season of the 
year, the prevailing wind, the barometer, and the thermometer, all 
had an infiuence on the result. Fortunately, the subject is not so 
complex as this experimenter would have us believe; I have found 
that, provided the insulation and the state of the surfaces be 
attended to, the season of the year, the barometer, the thermo- 
meter, and the prevailing wind may be left out of account. It is 
* Ann. de Chim., vol. viii. (1818). t Exp. lies., art. 2141. 
+ Journal de Physique (1811). 
