12 Mr . Cavallo’s Magnet ical 
In order to put this projed to the trial, fix magnetic bars 
were fo difpofed in an oblong earthen veflel, as that the north 
poles of three of them might be oppofite the fouth poles of 
the three others, forming two parcels of bars, lying in the fame 
direction, and about three inches afunder, which nearly was the 
length of the fleel bar which was intended to be rendered mag- 
netic. Things being thus difpofed, the fleel bar was made 
quite red hot, and in that date was placed between the mag- 
netic bars ; after which cold water was immediately poured 
upon it, which rendered it fo hard as not to admit being 
filed : its magnetifm was found to be confiderably ftrong, but 
by no means extraordinary. From repeated trials with fleel 
bars of different fizes, and by ufing a greater or lefs number of 
magnetic bars, I found, that fhort fleel bars acquire a propor- 
tionably greater degree of magnetifm by this method, than 
thofe which are longer ; that the magnetifm in the longer bars 
is not proportionably as ftrong, principally becaufe the arti- 
ficial magnets being placed at their extremities have very little 
power on thole parts of the pieces of fleel which are nearer its 
center; and, laftly, that when, in order to remedy the juft 
mentioned impediment, more magnets are placed nearer the 
middle of the fleel bar, then this piece of fleel generally 
acquires many lucceflive magnetic poles. 
Upon the whole it feems, that though this method alone he 
not lufficient to communicate to fleel bars an extraordinary 
degree of magnetifm, yet it may be of great ufe in conflrudling 
large artificial magnets ; for if thofe bars, inftead of being 
hardened in the ufiual way by plunging them when red-hot 
in water, be hardened whilfl Handing between powerful 
magnets, they will thereby acquire a confiderable degree of 
magnetic power without any additional trouble to the work- 
men. 
