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XXXV. April 21, 1772. Rxperhnents on 

 two Dipping - Needles , which Dipping- 

 Needles were ?7tade agreeable to a Plan of 

 the Reverend Mr. Mitchell, F. R. 8. 

 Retlor ^Thornhill in Yorkshire, and exe- 

 cuted for the Board of Longitude ', by Mr. 

 Edward Nairne, o/'Cornhill, London. I 



Read July 9, ^ g 1HE magnetic needles were twelve 

 1 inches long, and their axes (the 

 ends of which were of gold allayed with copper) 

 refted on friction- wheels of four inches diameter, 

 each end on two friction-wheels, which wheels were 

 balanced with great care. The ends of the axes of 

 the fri&ion-wheels were likewife of gold allayed 

 with copper, and moved in fmall holes made in 

 bell-metal j and oppofite the ends of the axes of the 

 needles, and the fricl ion- wheels, were flat agates, 

 finely polimed. Each magnetic needle vibrated in 

 a circle of bell- metal, divided into degrees and half- 

 degrees, and a line paffing through the middle of 

 the needle to the ends pointed to the diviflons. The 

 minutes fet down in the experiments were, by esti- 

 mation, as the third of half a degree is counted ten 

 minutes. The inftruments were carefully placed, fo 

 that the needles vibrated exactly in the magnetic 



meridian. 



