Obfervations in Electricity. 139 
the electricity. Perhaps a tenor or bafs-viol might pro- 
duce the effect in a greater degree. 
5. Mr. cavallo likewife informs me, that taking two 
pieces of broken China ware, he ftruck the edges of 
them brifkly together, and produced fparks of fire, but 
no electricity. He then rubbed the broader furfaces 
gently together, and produced a ftrong e left rid ty ; pofi- 
tive in one piece, negative in the other. This experi- 
ment I have feveral times repeated to my entire fatif- 
f aft ion. 
6. 1 have myfelf obferved,that two glafs tubes, nibbed 
brifkly together, produce a vivid purple light and ftrong 
phofphoreal fmell, but no attraction or repulfion; but 
two pieces of plate glafs, each two inches long and one 
inch broad, warmed and rubbed gently againft each 
other, produce electricity, negative in one piece, pofitive 
in the other. Both glafs and amber I have alfo made 
eleCtrical by blowing upon them (previoufly warmed) 
with a pair of bellows. 
7. Platina, in the pureft ftate to which it could be re- 
duced by chemiftry, and on w'hich Dr. lewis informed 
me that the ftrongeft fires he could raife had no further 
effeCt, I have been able to fufe in a fmall degree, by a 
ftrong charge of electricity. Phil. Tranf. vol, LXIV. 
p. 416. 
T * 
8 . Since 
