Ixvi INTRODUCTION TO THE MAKERSTOUN OBSERVATIONS, 1845 anp 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. XXVil. 
119. In addition to these observations, others were made in 1846 and 1847, 
according to Dr Lamonv’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 Tuomas 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 Jongs), 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 :— 
TasLE 13.—Fifth series of Observations for the Induction Coefficient at Makerstoun, 
of the Makerstoun Collimator Deflection Magnet, September 15, 1847. 
+e Interpolated 4 
Position A De Difference 
of Bifilar Reading, DEhection® Sum of of Value of dm 
manectors Reading. Deflector Deflections. Deflections. m 
Away. 
So. Diy. So. Div. Se. Diy. Se. Div. Se. Div. 
Away. 188-35 
N. Pole N. 10-67 188-11 177-44 : 
N. Pole S. | 363-65 | 187-87 | 175-78 | 393-22 LEG. q ip Qian 
Away. 187-62 
N. Pole N. 10-32 187-43 177-11 
N. Poles. | 362-90 | 187-24 | 17566 | 2277 came sr = 
Away. 187-05 
N. Pole N. 9-80 187-02 177-22 
N.PoleS. | 36257 | 186.99 L7ESB Ol Re 1:64 000 ee 
Away. 186-95 
N. Pole N. 9.65 186-80 177-15 
N.PoleS. | 36242 | 18665 | 175-77 | 35292 oe O-mnsae 
Away. 186-50 
N. Pole N. 9-25 186-43 177-18 , 
N. Pole S. | 361-90 | 186.36 | 175-54 | 392-72 1S | eo 
Away. 186-30 
N. Pole N. 9-25 186-33 177-08 | 
N.PoleS. | 362-00 186-36 175-64. |) oe? Te | oe 
Away. 186-40 
The angle of torsion of the bifilar was, » = 53° 45’. 
The arc value of one scale division, = 1/025. 
