Ixvi Introduction to the Makerstoun Observations, 1845 and 1846, 



The observations, therefore, for the absolute value of X in 1844 and 1845-6, 

 shew rather less secular change than is indicated by the bifilar magnetometer. See 

 Introduction for 1844, p. xxvii. 



119. In addition to these observations, others were made in 1846 and 1847, 

 according to Dr Lamont's modification, with small magnets and instruments con- 

 structed by Mr Jones of London. The observations of deflections will be found, 

 p. 349-351 ; and the results for the observations of vibration, p. 352. 



120. The determinations of the torsion, induction, and temperature coefficients, 

 were performed in a similar manner to those for the large bar. As the observations 

 for the induction and temperature coefficients may have some value independently 

 of their direct application, they will be given somewhat at length. 



121. Observations of deflection were made June 23, 1846 and January 2, 1847, 

 with a six-inch circle magnetometer (belonging to Professor Forbes), and May 31, 

 June 15, September 11, and September 13, 1847, with a nine-inch circle magnet- 

 ometer belonging to Sir Thomas Brisbane. The observations for the induction 

 coefficients were made with the nine-inch circle, fitted with a bifilar torsion circle 

 and magnet with mirror parallel to its axis (lent by Mr Jones), and in a manner 

 precisely similar to those for the large bar described. Introduction, No. 26. The 

 following table contains a specimen of the results : — 



Table 13. — Fifth series of Observations for the Induction Coefficient at Makerstoun, 

 of the Makerstoun Collimator Deflection Magnet, September 15, 1847. 



Position 



of 

 Deflector. 



Bifilar 

 Reading. 



Interpolated 



Reading, 



Deflector 



Away. 



Deflection. 



Sum of 

 Deflections. 



Difference 



of 

 Deflections. 



Value of 



m 



Away. 



N. Pole N. 



N. Pole S. 



So. Div. 



188-35 



10-67 



363-65 



Sc. Div. 



188-11 



187-87 



Sc. Div. 



177-44 

 175-78 



Sc. Div. 



353-22 



Sc. Div. 



1-66 



0-00470 



Away. 

 N. Pole N. 

 N. Pole S. 



187-62 



10-32 



362-90 



187-43 

 187-24 



177-11 

 175-66 



352-77 



1-45 



0-00411 



Away. 



N. Pole N. 



N. Pole S. 



187-05 



9-80 



362-57 



187-02 

 186-99 



177-22 

 175-58 



352-80 



1-64 



0-00465 



Away. 



N. Pole N. 



N. Pole S. 



186-95 



9-65 



362-42 



186-80 

 186-65 



17715 

 175-77 



352-92 



1-38 



0-00391 



Away. 



N. Pole N. 



N. PoIp S. 



186-50 



9-25 



361-90 



186-43 

 186-36 



177-18 

 175-54 



352-72 



1-64 



0-00465 



Away. 



N. Pole N. 



N. Pole S. 



186-30 



9-25 



362-00 



186-33 

 186-36 



177-08 

 175-64 



352-72 



1-44 



0-00408 



Away. 



186-40 













The angle of torsion of the bifilar was, v = 53° 45'. 

 The arc value of one scale division, = r-025. 



I 



