xxxii INTRODUCTION TO THE MAKERSTOUN OBSERVATIONS, 1845 AND 1846. 
43. The arms of the torsion circle were turned during disturbances,* as follows : 
Se. Div. 
1845. Apr. 18415 Om™— 46m B= —T1° 12’ A= —658 B=1:052. 
1845. Apr. 13" 15" 46™—21" 30™ B= —0°9'5 A= — 8:5. 
The arms of the torsion circle were turned to their original position at April 
134 21" 30”. 
Se. Div. 
1845. Dec. 347" Qm— 49m B= + 3°13'5 A= +1600 B=0-°857. 
1845. Dec. 3475 49m— 44215 B= —O° 65 A=— 55. 
The arms of the torsion circle were turned at Dec. 4¢ 23", to within 1’ of the 
original reading ; the observations from that time till January 1, 1846, have been 
corrected by — 10 sc. div. for this error of torsion circle reading. 
1846, January 1734", 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° 165 
to 109° 31’, or through 45'-5, the angle v being changed from 68° 18’ to 69° 35. The 
constants for reducing the observations after January 1, 1846, to scale divisions of 
the same value as in 1844 and 1845, are 
1846. B= + 0°45°5 A= + 39°7 se. div. B = 0:967. 
These reductions have not been made, but the observations from January 04 
13", 1846 to 1¢ 38 have been reduced by the quantities 
A = — 39°7 se. 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 se. 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 (corrected for temperature 
+ 300) = 5087; 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, 2 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 smal] 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. 
