188 PHILOSOPHICAL TRANSACTIONS. [anNO I667. 



Anno 1 630, in several places of Paris, and found that the needle declined 44- 

 degr. north-east : this I made known here to the curious and to artists, some of 

 whom counted nine or 10 degrees, according to the tradition and writings of 

 Orontius Fmeus and Castelfranc ; others 114^ degrees, following Sennertus and 

 OfRisius. 



You know that Gilbert, though the first who has written rationally on the 

 magnet, asserts towards the end of his book, that if a magnet altogether round 

 were placed on a meridian, and its poles so placed as to answer to the poles of 

 the world, and consequently its axis to the axis of the world, the stone would 

 continually of itself turn round in 24 hours. Whence he infers that the whole 

 earth, as a great magnet, turns also round about its axis in the same space of time. 



To try the truth of this proposition, I caused a magnet to be turned with the 

 powder of emery of a spherical form, with all possible exactness, of l-i- inch in 

 diameter; which, on account of its compact and uniform composition, had its 

 three centres of magnitude, gravity, and magnetism all the same, with so much 

 justness, that after I had exactly found the two poles of this stone, I caused two 

 «mall holes to be made therein, to support it by two points of needles, as by two 

 pivots : which having put in a meridian of brass, and suspended the ball between 

 them like a little globe, it was so easily moveable that I made it turn every way 

 with a blast only of my mouth, and it stopped indifferently, now in one, then in 

 another place, not any side of it prevailing by its gravity, nor descending as it 

 would have done, if any of them had been heavier than another. 



This stone thus prepared, without any defect in virtue or figure, uniform, 

 homogeneous, equilibrated, being adjusted on its meridian, and a horizon so 

 placed on its meridian line, that the poles answered to the poles of the heavens, 

 the result was that it had not any motion, and a small white mark I had made 

 upon this stone remained still in the same place where I had put it without 

 turning at all : whence I thought the proposition of Gilbert sufficiently re- 

 futed. 



This stone, together with a greater one, served also to find out whether the 

 needles touched in different places, nearer to or further from the poles, had 

 different declinations. Which having tried frequently with these, and with 

 other stones, I found no difference at all in the declination of the needles, 

 which in all of them was 4-1- degrees from the north-eastward. And as I did not 

 suspect that this declination would have changed, having found it to be the 

 same in many places, from Brest in Brittany to the Valtaline among the Alps, 

 I believed the ancients had ill observed, and that the want of their exactness in 

 respect either of the meridian line or the fabric of their needles, or the division 

 of their circles, was the cause of this defect. But I was soon undeceived of my 



