offufpending Magnet leal Needles. 54$ 
I fhould think, that there could be no great difficulty 
to adapt to thefe kind of needles a thin glafs, metallic, or 
enamelled plate, ferving inftead of the card in the com- 
mon nautical compafles, and to make ufe of them in azi- 
muthal compafles. 
A card, if it is not required to be ftuck upon the nee- 
dle, might be fixed to the bottom of the glafs bafon de- 
ftined for this apparatus. 
Common water would be, perhaps, the belt medium 
for thefe different contrivances, if fteel was not fo eafily 
rufted by it, if the needle was covered with fome varnifh 
or metal unalterable in water, and if in cold weather it 
was not fo apt to freeze ; and therefore, I think, fome of 
the thinned: exprefled oils would anfwfer the purpofe bet- 
ter. Linfeed oil, when it has fubfided, is very clear and 
tranfparent, and is not fubjedt to freeze, at leafl in the 
common cold of our climates; befides, it increafes the 
magnetical power of fteel, as Dr. knight found. If 
it thickens by time, it may be changed. 
The glafs bafon containing fuch a compafs fhould be 
kept full of the liquid to the cover, to obftrudt undulat- 
ing motions. 
The plate joined to this paper is not made to ferve as a 
model of a compleat apparatus, as the drawing was made 
from, i 
