INTRODUCTION. XIX 
The following are the corrections which have been applied to the observations 
of declination, on account of the estimated torsions ; the first value of = applying 
only to the observations before May 234 20", 
Period. Torsion. Correction. 
3 Se. Diy. 
May 164 23232 5h, 180 +163 
May 234 20h—304 204, 249 +19°5 
May 304 23h, 160 +12°5 
May 314 2h—5h, 40 + 32 
May 314 20h—June 2! 5h, mays + 2:9 
June 24 20h—June 34 5h, 9 — 0.7 
June 64 20h, Two fibres found broken ; they were cut off and the torsion removed. 
June 204 21h, Torsion tried ; found to be 61° 30’. 
June 262 20%, Fibre broken ; removed the torsion which was 173°. 
June 284. The torsion is always determined and removed during the period of 
dip observations. For these determinations, see notes to the Daily Observations. 
July 184 20". Fibre broken ; the torsion was removed as nearly as possible for 
the day’s observations. 
July 19* 5", The thread, prepared May 264, and having a brass weight sus- 
pended since then, was now inserted, the other having become weak. This thread 
was composed of 20 fibres. The torsion was completely eliminated this evening, 
19. Errors from accidental sources. 
It is believed that a small magnet intended to be placed in the brass bar to 
facilitate the elimination of torsion from the suspension thread of the declinometer, 
but which was never used, had been lying in the writing-desk between July 1841 
and March 29. 1843. The position of the desk was to the east of the reading tele- 
scope of the declinometer, except on term-days, when, for convenience, it was moved 
to a position nearly midway between the piers of the Declination and Balance 
magnetometers. 
In the usual position of the desk, the greatest effect of the small magnet on the 
declination might be from + 0/-2 to — 0”2 ; and during term-days from + 1/1 to — 1/1, 
It is probable that the magnet remained in the same position in the desk fora long 
period. 
The effect would be constant for each term, and from term-day till term-day. 
ABSOLUTE DECLINATION. 
20. The absolute declination is determined in the following manner :— 
The middle wire of the theodolite telescope is brought to coincide with the 
