Inteoduction. xxvii 



June 24*^. After several trials, the plane of detorsion and the magnetic meri- 

 dian were found to coincide when the torsion circle read 269° 5Q'. 



The weight being attached, the arm of the torsion circle was turned 90° — its 

 reading being then 359° 56' ; the collimator was turned by its independent motic n 

 till the scale read ISO*^''. The magnet being substituted, N. pole East, it was found 

 requisite to turn the arms of the torsion circle 70° 4', to make the scale again read 



Magnet at right angles to magnetic meridian. Scale reading 130<*. Torsion 

 circle reading 70° 0^ 



V = 70" 4' a = l'-1233 = -0003268 in parts of radius k = a coi v = 0-000185 



In this position of the magnet, N. pole towards the east, increasing scale read- 

 ings indicated decreasing force, this has been reversed in the reduced observations, 

 which were subtracted from a constant quantity. 



July 29d. The bifilar was readjusted, the N. pole of the magnet being directed 

 to the west, in order that increasing readings may indicate increasing force. 



The plane of detorsion and magnetic meridian coincided when the torsion circle 

 read 269° 52'. The brass weight being suspended, the arms of the torsion circle 

 were turned 90° ; circle reading 179° 52'. The collimator scale was made to read 

 153-3'^'\ The weight being removed, and the magnet substituted, the arms of the 

 torsion circle were turned 65° 2'; circle reading 114° 50' ; the scale reading was 

 153*". 



V = 65" 2', /*; = 0-0001185 



Sept. 7*^. The readings of the scale being always considerably above the zero 

 division (153), the arms of the torsion circle were turned 50'; the circle reading 114° 0'. 



V = 65" 52/ k = 00001464. 



Mr Russell could not make any conjecture as to the difference between the 

 values of -y, obtained June 24*^ and July 29*^. Professor Lloyd, with whom he 

 communicated, suggested a twist in the wires as the probable cause ; this Mr Rus- 

 sell found to be the case. 



Oct. V^. Wlien the magnet was removed, and the weight suspended, afterwards 

 the weight and collimator being lifted off the grooved wheel, the wires turned 

 sharply round towards the east. 



The old wire was removed, and great pains taken to obtain one free of twist ; 

 six wires were, in succession, rejected; for, though prepared with great care, very 

 different values of v were obtained, according as the magnet was placed with its 

 N. pole easterly or westerly. After much trouble and trials in every way, a wire 

 was got which gave satisfactory results after pegging the extremities and winding 

 up (fertile sources of twist). The wires kept nearly the same position with light 



