VOL. XL.] PHILOSOPHICAL TRANSACTIONS. 247 



15 years in an erect position, had acquired a fixed pole at top, so that the end 

 which had stood uppermost attracted the north end of a compass-needle, and 

 the other end the south end of the needle; and having susjjended it by a string 

 for the space of half a year, it acquired a fixed south pole at that end, as well 

 as it had done at the other in the time of 15 years, without diminishing the 

 virtue of the other end : so that both ends of the rod in any situation attracted 

 the north end of the compass-needle. 



That rods of iron untouched, or which have not acquired a magnetic virtue 

 by their situation, will with their upper end, whatever end of the bar be held 

 upwards, attract the north end of the needle, and the lower end of the bar 

 the south end of it, is a truth known many years ago, and mentioned in Dr. 

 Brown's book of vulgar errors. 



SoTne further Magnetical Experiments made before the Royal Society. By 

 Dr. Desaguliers. N° 430, p. 386. 



It is well known, and has been often found by experience, that an iron bar 

 untouched by a loadstone, will, with its upper end, attract the north end of 

 the needle of a compass, when the said bar is held upright, and the south end 

 of the needle with its lower end, when applied to it, still in a perpendicular 

 position, whatever end of the bar be held up ; unless the bar has acquired a 

 fixed pole by having been long in a vertical position. But if the bar, from a 

 vertical, be brought to a horizontal position, the needle will return into the 

 situation it had before, which was in the magnetical meridian, the bar being 

 then at right angles to it. On raising or sinking the end of the bar which is 

 farthest from the needle, the one or the other end of the needle will begin to 

 move towards the bar. Such a bar has in itself no fixed magnetic virtue; but 

 if it had, it must be heated red-hot, and then cooled in a horizontal position. 

 A bar thus prepared, is fit to make the following experiments, communicated 

 by M. du Fay. 



Hold the bar upright, and give it a blow or two against the ground with its 

 lower end ; and that end will attract the south end of the needle, when the 

 bar is held horizontal, and at right angles to the magnetic meridian : the other 

 end held horizontal in the same manner, will attract the north end of the 

 needle. Invert the bar, and its virtue will be lost by striking as many blows 

 with it against the ground with the other end : then strike another blow or 

 two, and the end which attracted the north end of the needle, will now attract 

 the south end ; and so vice vers&, the position being still horizontal. , 



