on the rubbing of a piece of iron on a loadstone in places midway between the poles, and upon the æquinoctial of a terrella.

s elect a piece of iron wire of three digits length, not touched by a loadstone (but it will be better if its acquired verticity be rather weak or have been damaged in some way); touch it and rub it on the æquator of a terrella, exactly on the æquinoctial line in the direction of its length, on the one end, or the ends only, or in all its parts; place the wire touched in this way on water in a cork fitted for it; it will swim about doubtfully on the waves without any acquired verticity, and the verticity previously implanted will be disturbed. if, however, it float by chance toward the poles, it will be checked a little by the poles of the earth, and will at length by the influence of the earth be indued with verticity.