f 5°9 ] 
tom was above three Fingers Breadth in Thicknefs, 
and that flew with as much Eafe at lead as the thin- 
ned Glafs. I have had fome others equally thick 
all over ; thefe have flown alfo, but with more Diffi- 
culty than the others. 
Thefe Glades are capable of redding very hard 
Blows coming from without : I have given to fome, 
with a Mailer, Strokes fufficicnt to drive a Nail into 
Wood tolerably hard, and they have held good with- 
out breaking. They alfo redd the Shock of leveral 
heavy Bodies, that are let fall into their Cavities. Thus 
I have dropped, from the Height of two or three 
Feet, Musket-balls, Pieces of Iron, Brafs, Tin, Silver, 
Gold, Antimony, Bilmuth, Pyrites, Jafper, and fe- 
veral Sorts of Woods, Ivory, and Bone : All which 
is indeed no- ways extraordinary ; for other Glafies 
equally thick would alfo bear the Strokes of the fame 
Bodies; but herein condds what is more furprifing. 
I took a Shiver of Flint, of the Size of a fmall 
Pea ; I let it fall into the Glafs from the Height of 
three Inches ; and in about two Seconds the Glafs 
flew. And having repeated the fame Experiment 
upon fcveral other Glafies with the fame Piece of 
Flint, the greatefl; Part broke in the Moment of the 
Shock, and the others one or two Seconds after it. 
I have let fall into different Glafies a Shiver of 
Flint, of but half the Size of that ufed in the former 
Experiment, and the Glafies flew in the fame Man- 
ner. 
Another Bit of Flint, of the Size of a fmall Len- 
til, has alfo produced the fame Effed. 
Being encouraged with this Succefs, I let fall into 
one of my Glafies a Piece of Flint no larger than 
a Grain 
