( 1 8 ) 
when that River was frozen over for feveral Miles, and 
Booths andStreets were made on the Ice, an Ox roafted 
thereon, &c. For the lowed Point of Freezing in 1716, 
was on January 7, when the Spirits fell to 3? Degrees 
only of the Glafs I now make ufe : But the true 
Caufe of the freezing of the Thames that Year was not 
barely the Excefsof the Cold, but the long Continu- 
ance of it : Which was alfo the principal Caufe of 
thofe remarkable Congelations of that River in 1683 
and 1708, when I faw Coaches driven over the Ice, 
large Fires made on it, I am, with great Re- 
fped. 
Honoured SIR, 
Tours , 
- . ^ . _ ' • f ■ f • T . - V; ' f 
William Derham. 
V. A Letter to Cromwell Mortimer, M. D. 
Seer. 5^. 5. containing federal Experiments con- 
cerning Electricity 3 by Mr. Stephen Gray. 
SIR, 
I N the Year 1719 I communicated to Dr. Defagu - 
Iters, and fome other Gentlemen, a Difcovery I 
had then lately made, (hewing that the EleCtrick Ver- 
tue of a Glafs Tube may be conveyed to any other 
Bodies, fo as to give them the fame Property of attract- 
ing 
Upmnfter t Feb. 
13 th, i73f* 
