xxxii 
Introduction to the Makerstoun Observations, 1843. 
turned through 69° 44', reading A 287° 44', the scale reading being 148. The 
westerly declination during adjustment was 25° 28'. 
November 8 d 21 h 20 m . The bifilar magnet was removed in order to determine its 
temperature correction ; the brass weight being substituted, the arms of the torsion 
circle were turned from A 287° 44' to A 357° 30', when the collimator scale read 
157*5, or 9*5 scale divisions greater than on April 28, the westerly declination being 
25° 20'. As it is necessary to determine the changes of horizontal force during the 
observations for the temperature correction, the magnet used for deflections in ob- 
servations of absolute horizontal intensity was substituted. The moment of this 
bar was found too great for grooved wheel No. 8, previously in use (Introduction, 
1841-2. 30.), wheel No. 9 was substituted, whose diameter = 0*459 inch ; as the 
diameter of wheel No. 8 = 0*409 inch, and the value of one division of the micro- 
meter-headed screw = 0*0005194 inch, the wires were rendered parallel by turning 
the micrometer head through 96 divisions. 
The brass weight being suspended, the scale reading was 128*5 
The magnet 126 0 
The weight being suspended, the arms of the torsion circle were turned through 90°, 
when it read, vernier A 178° 0', B 358° 0' ; the collimator was then turned by its 
independent motion till the scale reading was 143 ; the magnet was suspended, and 
the scale reading was found 142 when the arms of the torsion circle were turned 
through 55° 17'*5, the circle reading A 122° 41'*5, B 302° 43'. 
November 10 d 6 h . The temperature experiments having been made, the de- 
flecting bar in the bifilar magnetometer was removed, and the arms of the torsion 
circle were turned from B 302° 43' to B 358° nearly, when the scale reading was 143, 
as in the previous adjustment. Wheel No. 9 was removed, and No. 8 substituted, 
the micrometer head being turned backwards through 96 divisions. 
The bifilar magnet being suspended, the scale reading was 93 
The brass weight 96 
the arms of the torsion circle were turned through 90°, when the reading was B 
358° 35' ; the collimator was turned by its independent motion till the scale reading 
was 172*4, the magnet was inserted and the arms of the torsion circle turned through 
68° 18', when the torsion circle reading was B 290° 17', and the scale reading 173°. 
The bifilar thermometer 42°*4, and the absolute westerly declination 25° 18'. 
39. The following are the values of v, of k = a cot v, and of q =-|, with the 
periods to which they apply in 1843. 
