XXXiV INTRODUCTION TO THE MAKERSTOUN OBSERVATIONS, 1843. 
or adapting the first constant to logarithmic computation 
ais 
B cos (v + (3) 
Nim aoe (0 +=) +R epanane nthe 
= A +n”nB +t 
8 is considered negative when v is diminished, n is negative when the reading is 
below the zero, and ¢ is the temperature of the magnet minus 26°. 
42. It was necessary to turn the arms of the torsion circle once only in 1843, 
namely, on 
May 67 10" 45", when vernier B was turned from 287° 44’ to 291° 45’, whence 
B=—4° 1’, A=234-7 scale divisions, B=1:19, v being=69° 46’. 
May 6° 13" 45™, the arms of the torsion circle were turned from B 291° 45’ to 
B 287° 41’, as this was 3’ different from the original reading, 3 scale divisions were 
subtracted from the abstracts of the observations from April 25% 2° till May 64 10°, 
the two hourly and extra observations are, however, affected to that amount. 
43. The effect of the balance needle upon the readings of the bifilar was deter- 
mined, September 47 1843, to be —4:03 scale divisions ; no correction has been ap- 
plied ; the effect of the declination magnet is zero, and the effect of the copper ring 
or damper has not been determined, but it is supposed to be small. 
44. Time of vibration of the bifilar magnet. 
8. 
Feb. 22. Mean of 88 vibrations, 1 vibration = 26:18 
March 1. Mean of 28 vibrations, 1 vibration = 26:25 
June 1. Mean of 27 vibrations, 1 vibration = 27:08 
Oct. 25. Mean of 8 vibrations, 1 vibration = 26:99 
Oct. 25. Another series, ; ; : 27:03 
45. The natural are of vibration is generally very small, and when considerable 
the time of vibration is found different from that determined by artificial vibrations 
(Introd. 1841-2, p. xxix), namely, about 25 seconds, which has been used in the 
observations. The observations are made as follows :—the point of the scale coin- 
ciding with the vertical wire of the fixed telescope is estimated to a tenth of a divi- 
sion at 25° before the minute of observation, at the minute, and 25° after it; the 
a =: - a, b, 
and ¢ being the three readings. The mean thus obtained is corrected to the tempe- 
rature of 26° Fahr., this being below the lowest temperature which occurred within 
the Observatory in 1843 ; a constant quantity of 300-0 has been added to all the cor- 
rected means. Tables were formed giving the temperature correction for every 
tenth of a degree above 26° from the formula (t—26) q'+ 300-0. 
46. The temperature of the magnet was obtained till November 274 18" from 
the thermometer by Ross, after that time from the thermometer by Messrs ADIE 
mean reading is deduced from the three readings by the formula 
