[ 2 9 ° ] 
If the needle, when ftruck, lies eaft and weft, the 
end enter'd by the electric blaft points north. 
If it lies north and fouth, the end that lay towards 
the north, will continue to point north, when placed 
on water, whether the fire enter’d at that end, or 
the contrary end. 
The polarity is given ftrongeft, when the needle is 
ftruck lying north and louth ; and weakeft, when 
lying eaft and weft. 
Perhaps if the force was ftill greater, the fouth 
end, enter’d by the fire, when the needle lies north 
and fouth, might become the north ; otherwife it 
puzzles us to account for the inverting of compaftes 
by lightning ; fince their needles muft always be 
found in that fttuation, and by our little experiment, 
whether the blaft enter’d the north, and went out at 
the fouth end of the needle, or the contrary, the 
end, that lay to the north, ftill fhould continue to 
point north. I have not yet had time to read and 
confider Dr. Knight’s E/Jays , juft now received from 
you, which poftibly may explain this. 
In thefe experiments the ends of the needles are 
fometimes finely blued, like a watch-fpring, by the 
eledtric flame. This colour given by the flafti from 
two jars only, will wipe off; but four will fix it, and 
frequently melt the needles. I fend you fome, that 
have had their heads and points melted off by our 
mimic lightning, and a pin, that had its point melted 
off, and fome part of its head and neck run. 
Sometimes the furface on the body of the needles is 
alfo run, and appears blifter’d, when examined by a 
magnifying glafs. The jars I make ufe of hold 7 
or 8 gallons, and are coated and lined with tin-foil. 
Each 
