VOL. XLIII.] PHILOSOPHICAL TRANSACTIONS. 73 



marked, by the rubbing of a piece of silver upon it, as on a touchstone: after 

 which, Mr. Knight carried the stone into his study; and reproducing it in about 

 a minute, showed that the poles were then directly inverted; and that the same 

 end, which before attracted the south end of the needle, now attracted the north, 

 and repelled the south, and vice vers^. 



After this, Mr. Knight again taking the stone, brought it back in as short a 

 time as before, with the direction of its polarity turned at right angles to its former 

 direction, and into the direction of the natural grain of the stone, the poles now 

 lying in the flat ends of the cylinder; one of which, being the smoother end, at- 

 tracted the south end of the needle, while the other, which was of a rougher 

 texture, attracted the north end, and repelled the south end of the same : when it 

 was also observed, that the polarity appeared stronger in this case, than either of 

 the former. 



Lastly, Mr. Knight, in about the same time, inverted this last direction of the 

 poles, keeping it still parallel to the axis of the cylinder, but causing the smooth 

 end of the stone to attract the north end of the magnetic needle, and the rough 

 end to attract the south, and repel the north end of the same needle. 



After this report, Mr. Knight proceeded to show, at the meeting, some of the 

 same artificial magnets there mentioned; and it was found, that the compound 

 magnet, consisting of 12 steel-bars, and which had, in the experiment made be- 

 fore the president, lifted 23 lb. 2i oz. Troy weight, did here, under all the in- 

 conveniencies and disadvantages of a crouded room, still lift a weight amounting 

 to 21 lb. 11 oz. 



It was also found, that the single armed block of steel, which had before 

 lifted 14 lb. 2 oz. did here, under the same disadvantages as the former, lift 

 13 lb. 7 oz. 



And lastly, Mr. Knight produced to the company the abovementioned natural 

 loadstone belonging to Mr. Hauksbee, but with the direction of its polarity again 

 altered from what it was, when it was last seen by the president. 



P. S. Since the artificial magnets mentioned in the foregoing paper, Mr. Knight 

 has caused some others to be made of a less size, but of a very great lifting power : 

 and one of these, weighing, without its armour, just an ounce, and with the 

 armour, cramps, and rings, 1 oz. 17 dwt. lifted 61b. 10 oz. 



This magnet consisting of 3 plates of steel, each 2 inches long, -^ of an inch 

 in breadth, and not above -^4^ of an inch in thickness: they were laid flat on each 

 other, and screwed together by 2 small brass screws going through the 3 plates. 

 After which, the little parallelopiped block so made up^ was armed with iron at 

 the 2 ends, cramped together with silver, and fitted with a double ring of the 

 samejmetal, for the cortvenient holding of it. 



VOL. IX. L 



