( }97 ) 
I. Two Letters from Mr. Stephen Gray, F. (f.S. 
to C. Mortimer, M &• Seer. ^ S. con- 
taining farther Accounts of his Experiments 
concerning Electricity. 
LETTER I. 
SIR, 
A CCORDING to my Promife, I herein give 
an Account of what farther I have difeover’d 
relating to Ele&rical Attraction, which I 
ftiould have done fooner, but was willing to fee what 
farther Improvement I could make to thofe Experi- 
ments, at my Return to London , which were begun 
in the Country. 
About the latter End of being at Mr .Whe- 
Jer's , after having repeated the Experiment of making 
Sulphur attraft Leaf-Brafs in vacuo , Mr. Wheler 
having a very good Air-Pump of the larger Sort, made 
by Mr. Hauksbee, we fufpended from the Top of a 
Receiver, which was firft exhaufted of Air, a white 
Thread that hung down to about the Middle of the 
fame: Then the Receiver being well rubbed, the 
Thread was attrafted by it vigoroufly. When it was 
at reft, and hung perpendicular, the Tube was rub- 
bed, and being held near the Receiver, the Thread 
was attrafted towards that Side of it' if the Tube was 
removed llowly, the Thread returned to the Centre 
of the Receiver, but when moved fwiftly, the Thread 
G g g was 
