t 2 5* ] 
2. They foretel the Weather by a much longer 
Space of Time than others, as moftly 20 Hours, fome- 
times 3 6 or 48 Hours: Nay, before great Tempefts, 
and fuch Rains as caufe great Floods, for a much 
longer time before they happen. 
3. Although they are fo fenfible of fuch minute 
Changes of the Air, yet the molt intenfe Heat will 
not raife them -a Haifs-breadth, nor the greateft Cold 
make them fall This fhews they arc perfed Baro- 
meters, and not in any degree Thermometers. 
4. You may by them diftinguifh whether, if they 
fhew for Rain, it will be little or much. 
y. As by other Barometers you cannot tell the 
Weather, but by a paft and a prelent Obfervation ; 
thefe tell you, the Inftant of Time you come to them, 
what the W eather is going to be : For by rapping the 
Cafe with your Finger, if it is going to be fair, or 
very fair Weather, the Mercury will rife that Moment 
a 10th of an Inch, or more: But if for foul, it will 
icarce make any fenfible Rife. 
[A.] TheReafon of this I fhall explain in the Ob- 
servations at the End, Rage 249. 
I have had one of the Glalfes by me for 10 Years, 
and have conftantly obferved its Motions, which has 
very feldom failed me in foretelling any confiderable 
Change of the Weather. 
But as fome People have fuch ftrange Notions, as 
not judging afterward whether they were told true or 
falfe, and others may mifs in their Expectations of per- 
fect Certainties, which none can attain to; it will 
not be improper to make the following 
Re- 
