[ 40i ] 
grees. The magnets were both covered with brafs 
weights of fixteen ounces each. Into the eaftern weight 
I poured about two ounces of boiling water j and the 
needle in one minute moved half a degree, and con- 
tinued moving weftward for about feven minutes, 
when it arrived at 2° f. It was then ftationary for 
fome time ; but, in twenty-four minutes from the 
beginning, it came back to 2° {, and in fifty minutes 
to 2° i. I then filled the weftern weight with boil- 
ing water, and in one minute, the needle came 
back to i° f j in fix minutes more, it flood half a 
degree eaftward ; and after that, in about forty mi- 
nutes, it returned to the magnetic north, or its firft 
iituation. 
It is evident, that the magnetic parts of the earth 
in the north on the eaft fide, and the magnetic parts 
of the earth in the north on the weft fide of themag- 
netic meridian, equally attract the north end of the 
needle. If then the eaftern magnetic parts are heated 
falter by the fun in the morning, than the weftern, 
the needle will move weftward, and the abfolute var- 
riation will increafe ; when the attracting parts of the 
earth on each fide the magnetic meridian have their 
heat increafing equally, the needle will be ftationary, 
and the abfolute variation will then be greateft ; but, 
when the weftern magnetic parts are either heating 
fafter, or cooling flower than the eaftern, the needle 
will move eaftward, or the abfolute variation will de- 
creafe ; and when the eaftern and weftern magnetic 
parts are cooling equally faft, the needle will again 
be ftationary, and the abfolute variation will then be 
leaft. This may be ftill further illuftrated, by placing 
the compafs and two magnets, as in the laft experi- 
Vo l. LI. F f f ment, 
