Iviii 
General Results of the Makeestoun Observations. 
The means of all the summer lunations indicate that 
The vertical component is a principal maximum about 3^ hours after the moon's inferior transit. 
minimum 8 hours superior transit. 
a secondaiy maximum near the moon's superior transit. 
minimum about 5 hours before the moon's superior transit. 
This last result serves very nearly for the mean of all the lunations in 1845, and for the mean of all the 
lunations in 1844, when the larger disturbances have been rejected as in the place cited above. 
Magnetic Dip. 
113. Observations for the absolute value of the magnetic dip were made with an instrument by Robinson in 
the years from 1841 to 1849 ; those till May 1843 were made with the instrument on a pillar near the declin- 
ometer (see Introduction, 1843, p. liv.) ; from June 1843 till February 1846, the obsei'vations were made in 
a small wooden house erected for the purpose about 19 yards north of the Observatory dip-pillar. The obser- 
vations after June 1843 were in general very unsatisfactory ; and ultimately, in February 1846, the observa- 
tions Avere discontinued (see section Inclinometer, in the Introductions to the various volumes, for details.) In 
order to determine the annual change of dip, the inclinometer was placed on the original dip-pillar in the 
Observatory in September 1849 ; previously, it was found, that both needles belonging to the instrmnent were 
much disfigured by rust ; the rust was removed as carefully as possible and the needles rebalanced. 
114. The following are the results of the observations, which were vei'y satisfactoi'y : — 
Sept. 281 23'> Needle No. 1. Dip = 71° 15'-93 
29<i 0^ Dip = 71' 14'-87 
29d 2^ Needle No. 2. Dip = 71° 16'-96 
29'' 5h Dip = 71° 16'-27 
115. The dip resulting from these observations differing to a considerable extent fi-om that obtained previously 
in the dip-house, the inclinometer was removed to that place in order to determine the value of the difference. It 
was found that the dip obtained on the Observatory pillar, was nearly five minutes less than that sliewn in tlie 
dip-house. Other observations were made immediately outside the Observatory, on the top, and at the NW. 
foot of the Observatory hill, which agreed almost exactly with those made on the Observatory pillar. The 
details of these observations must be reserved for another occasion ; it is believed, however, that the difference 
found for the first two places of observation is due to the wall of a sunk fence built of trap stones, which passes 
within about 2 yards of the instrument when in the dip-house, the top of the wall being on a level vath the 
sui'face of the ground. The following then are the means of all the observations of magnetic dip made -ivith 
the Makerstoun inclinometei ; the observations made in the dip-house between June 1843 and February 1846, 
having been corrected by — 5'. 
Table 55. — Mean Value of the Observations of Magnetic Dip. 
Dates. 
Mean Epoch. 
No. of 
Observations. 
Position of 
Inclinometer. 
Mean of 
Observed Dips. 
July —Dec. 1841 
Jan. —Dec. 1842 
Jan. —June 1843 
1841- 8 
1842- 5 
1843- 2 
27 
86 
36 
Observatory 
Dip-Pillar ' 
71 25-90 
2;5-95 
22-14 
June— Dec. 1843 
1843-7 
48 
20-20 
Jan. —Dec. 1S44 
Jan. —Dec. 1845 
1844- 5 
1845- 5 
67 
82 
Dip-house ■< 
2.3-69 
23-10 
Jan. —Feb. 1846 
1846-1 
12 
22-40 
Oct. 1849 
1849-7 
4 
Observatory 
Dip-PUlar 
16-00 
IIG. The observations made in the years 1841-2-3 on the Observatory dip-pillar, give for the meiui epoch 
1842-5, the mean dip = 71° 24'-0 ; those made on the same pillar 1849*7, give the mean dip = 7r 16'-0; 
wlience the change in 7*2 years = — 8'-0, or = — I'-ll a year. 
