22 Mr. Cavallo’s Magnetical 
after which the needle generally vibrated backwards and for- 
wards, but upon the whole it gradually receded. 
On repeating the experiment with a larger quantity of the 
mixture, and alfo with different proportions of ingredients, I 
could not obferve any particular attraction. The needle vibrated 
rather more than before, but gradually receded ; fo that at laffc 
it flood farther from the vefiel than it did before the mixture 
was fet on fire, though not quite in its natural direction. 
The vibration of the needle in this experiment, or its wav- 
ing motion, was probably owing to the irregular burning of 
the mixture, and perhaps to the heating of one part of it wbilft 
the other was burning. The gradual receding of the needle 
was certainly owing to the dephlogiftication of the iron. 
After having thus related the refult of experiments, I fhall 
now beg leave to add a few thoughts concerning the application 
of thole obfervations towards accounting for the variation of 
the magnetic needle. 
This wonderful phenomenon has, fince it was fir ft difcovered, 
employed the thoughts of very able philofophers ; many hypo- 
thefes having been offered, not only for its explanation, but 
even to foretel the future variations in various parts of the 
world. I need not detain this learned Society with a particular 
hiftory of thofe hypothefes, but (hall only obferve in general, 
that neither their predictions have anfwered, nor any of them 
was founded upon evident principles. The fuppofition of a 
large magnet being inclofed within the body of the earth, and 
of its relatively moving with refpeCt to the outward fhell or 
cruft ; the luppofition of there being four moveable magnetic 
poles within the earth ; the hypothelis of a magnetic power, 
partly within and partly without the furface of the earth ; toge- 
ther with feveral other hypothefes on the fame fubjeCt, are not 
only 
