A treatise of artificial magnets; in which is shewn an easy and expeditious method of making them superior to the best natural ones; and also, a way of improving the natural ones, and of changing or converting their poles. Directions are likewise given for making the mariner's needles. In the best form, and for touching them most adventageously, &c A treatise of artificial magnets; in which is shewn an easy and expeditious method of making them superior to the best natural ones; and also, a way of improving the natural ones, and of changing or converting their poles. Directions are likewise given for making the mariner's needles. In the best form, and for touching them most adventageously, &c