xxxii Introduction to the Makerstoun Observations, 1845 and 1846. 



43. The arms of the torsion circle were turned during disturbances,* as follows : 



Sc. Div. 



1845. Apr. IS-i 15^^ O"'— 46"^ /3 = - 1° 12' A = - 65-8 B = 1-052. 

 1845. Apr. 13^ IS^^ 46''^2P 30"^ (3= - 0° 9'-5 A = - 8-5. 



The arms of the torsion circle were turned to their original position at April 

 131 2P .30°'. 



Sc. Div. 



1845. Dec. 3'* 7" 2^— 49™ /3 = + 3° 13'-5 A = + 160-0 B = 0-857. 

 1845. Dec. S^ 7^ 49'"— 4<i 2^^ /3 = - 0° 6'-5 A = - 5-5. 



The arms of the torsion circle were turned at Dec. 4'* 2^^ to within 1' of the 

 original reading ; the observations from that time till January 1, 1846, have been 

 corrected by — 1*0 sc. div. for this error of torsion circle reading. 



1846, January 1** 3^**, On account of the readings of the bifilar approaching 

 too near the top of the scale, the arms of the torsion circle were turned from 110'' 16*5 

 to 109° 31', or through 45''5, the angle v being changed from 68° 18' to 69° 3''5. The 

 constants for reducing the observations after January 1, 1846, to scale divisions of 

 the same value as in 1844 and 1845, are 



1846. ^= + 0°45'-5 A = + 39-7 sc. div. B = 0-967. 



These reductions have not been made, but the observations from January 0** 

 13*", 1846 to 1*^ 3** have been reduced by the quantities 



A = - 39-7 sc. div. B = 1-033 



to the same scale values as the other observations in 1846, and in the abstracts the 

 observations for 1846 have been rendered comparable with those for 1845 by the 

 following process : — The scale reading immediately before turning the arms of the 

 torsion circle was 218-7, therefore n = 48*7 sc. div. ; and from the constants A and B 

 and the previous formula, N = 9*3 sc. div., whence the readings after the adjustment, 

 the horizontal force remaining constant, should have been 179*3, the temperature of 

 the magnet being 40°-9, the tabular reading before adjustment (corrected for tempera- 

 ture + 300) = 547*0, and the reading after adjustment (con-ected for temperature 

 + 300) = 508*7 ; since these two readings are for the same value of the horizontal 

 force and the zero for 1845 is taken in the abstracts of the results as 500, z the zero 

 for 1846 will be obtained from the equation 



(547-0 - 500-0) 0-000140 = (508-7 - z) 0-000135 

 whence z = 460*0. 



* In 1847, it was found more convenient during disturbances, to bring the scale of the bifilar 

 magnet into the field of the reading telescope, by means of a small deflecting magnet placed on a 

 beam of wood at known distances from the centre of the bifilar magnet. The effect of the deflecting 

 magnet was afterwards determined with the aid of a second deflecting bar. 



