xxxii Introduction to the Makerstoun Observations, 1844. 



during a moderate magnetic disturbance ; the results are given as a specimen of the 

 accuracy that may be expected from this method. 



„ . Bifilar * (A»-AJ) , , M N , 



Date. rl . , u d , ori0 /., t q (t — tn) & 



Corrected. X cot 39 40' * v w 



Sc. Div. o / o / 



May7 d 22 h m 4799 -14 42-88 25 16-82 48-4 



23 30 533-0 -14 29-56 25 9-86 +0-007114 ^ -0-000063 0-0001328 

 8 1 32 571-9 -14 2028 25 400 +°-005331 ^ -0000084 0-0001344 

 The mean of the two values of £ = 00001336. 



In August 1847, a series of comparative observations were made of the bifilar 

 and a unifilar horizontal force magnetometer : these observations were made every 

 hour for three days ; the results were grouped so as to obtain the greatest differences 

 of readings for comparisons ; the mean angle of deflection of the unifilar (u—8) was 

 equal to 65°. The final result of the whole groups was, that the changes of the uni- 

 filar scale readings were to those of the bifilar scale readings as 1 to 0-974, the value 

 of k for the unifilar being 0-0001389, therefore that of k for the bifilar = 0-0001353. 

 The changes of horizontal force from which this result was deduced were small. 



38. The following, then, are the values of k, deduced by the five different pro- 

 cesses above : — 



Short deflector, E. and W. of bifilar magnet, and N. and S. of declination magnet, £ = 0-0001349 



N. and S E.andW £=0-0001353 



Large deflector, E. N.and S £ = 0-0001360 



S. E.andW £=00001353 



Comparisons of unifilar and bifilar horizontal force magnetometers, £ = 00001353 



The mean of all the results gives £ = 0-0001354 

 The adopted value of £=0000135 



39. The value of the coefficient deduced from the angle of torsion of the sus- 

 pending wire is 



1847. £ = a cot v = 0-00032675 x cot 69°-3' = 00001251. 



135 



The ratio of the true value of £ to that determined by the angle of torsion = = 1-08. 



40. The true values of k from 1841, obtained from the formula 1-08 x a cot v 

 are given below : — 



July ll d 20 h 1841— July 23 d 5 h 1841, £=0-000128 



Aug. 4 20 1841— Sept. 7 5 1841, £ = 0-000164 



Sept, 7 20 1841— Sept. 30 5 1841 £=0-000158 



Oct. 6 20 1841— Oct. 19 28 1841, £=0-000141 



Oct. 19 23 1841— April 27 4 1843, £=0000135 



April 28 2 1843— Nov. 8 22 1843, . . . . • £=0-000130 



Nov. 10 8 1843— Dec. 31 12 1844, £ = 0-000140 



