392 PHILOSOPHICAL TRANSACTIONS. [aNNO 1747. 



The tempered needle was then placed flat on the bars, so that nearly one half 

 of it rested on one bar, and the other half on the other, the cap lying between 

 the two. The needle was pressed close to the bars in this position ; after which 

 the bars were drawn away, both at the same time contrarywise, till thev were 

 clear of the needle ; and this operation was repeated 3 or 4 times : after which, 

 that end of the needle which had rested on the northern part of one of the bars, 

 was found strongly to attract the north end of the needle in the compass-box ; 

 and the other end, which had rested on the southern part of the other bar, was 

 found to attract in lilie manner the south end of the same needle in the box. 

 The power of attraction also acquired by this needle, appeared to be very consi- 

 derable, lifting easily with either of its ends, the two iron weights above men- 

 tioned, when cemented to each other with wax, and weighing together 1 oz. 

 10 dwt. 5 grains. The hard needle was then applied to the bars like the other, 

 and with the very same success, lifting also, as the other had done, both the 

 weights together. 



The 2 needles were then themselves applied to each other, first the northern 

 half of the one, in a contrary direction, to the northern half of the other ; and 

 then the southern half of the first, in a like contrary direction to the southern 

 half of the last ; and from these several positions, they were severally drawn till 

 they were clear of each other, and this several times successively : after which 

 operation it was found that the tempered needle had lost so far its virtue, that 

 its northern end had hardly any effect on the needle in the box ; that its south- 

 em end even began to attract the contrary end of the needle from what it did 

 before, and that it was no longer able to lift at either of its ends any sensible 

 weight. But as to the hard needle, that still retained a considerable share of its 

 former virtue ; its ends still strongly drawing the same ends of the needle in the 

 compass-box, as they drew before, and either of them lifting with ease the heavier 

 of the two above-mentioned weights. 



Mr. Knight then produced one of his common small magnetic bars ; which 

 being applied to the forementioned large bars, in the same manner as the needles 

 had been applied to the same, but in a position contrary to that of its present po- 

 larity, it had its poles thereby counterchanged or inverted, and was found to lift 

 at that which was now become its northern end, the weight of 6 oz. 8 dwt. 

 5 grains. 



Lastly he produced one of his large artificial armed magnets, composed of se- 

 veral thin plates of steel cramped together, with which he acquainted us he had 

 some time before lifted 36 pounds, and with which he did now actually lift before 

 us 31 lb. 9^ oz. 



The tempered needle mentioned above, and which had nearly lost all its virtu^ 

 had the same again restored in great measure, on being touched in the common 



