Dr. knight’s Magnelical Machine. 593 
fome circumftances, relative to this machine, which 1 do 
not know have been related either by himlelf or any 
other per fon. 
The firft thing, I believe, that engaged the dodfor’s 
attention more particularly to magnetiim, was the acci- 
dent that befel a {hip’s compafs from lightning; and 
of which, 1 think, the dodlor gave a very circumif antial 
account to the fociety. This affair led him to confider 
the ftrudlure of the compafs more minutely. He pro- 
cured compafs-cards ready-armed, as it is called, fiom dif- 
ferent makers both at home and abroad. He found molt 
of the needles ftrangely erring from due polarity; fome 
being many points to the Weft, others as many to the 
Eaft, of the right pofition. Amongft them all there was 
only one, which to him feemed conftradted on a rational 
plan, and was of French make, procured from Marfeilles ; 
but even this was not without very evident faults. 
To fix upon the proper form of a needle through which 
the magnetic effluvia could pafs with the leaft interrup- 
tion, to give the needle fuch a degree of hardnefs as to re- 
tain the magnetic influx the longeft, and with the greateft 
force, were material objedts; and, I imagine, a view 
to have fuch a degree of magnetic power at his com- 
mand, as to force the magnetic virtue through the moft 
confolidated bars, was his firft inducement to try, whe- 
ther he could not colled! fuch a magazine of magnetiim, 
as would be fufficient for every purpofe of this kind, 
and at the fame time exhibit fome new phenomena in 
phyfics 
