Iviii General Results of the Makerstoun 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 secondary 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 tlie instrument on a pillar near the declin- 

 ometer (see Introduction, 1843, p. liv.) ; from June 1843 till February 1846, the observations 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 were 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 instrument 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 very satisfactory: — 



Sept. 28d 2S^ 



29<i 0"^ 



29d 2*^ 



29*^ 5^ 



Needle No. 1. 

 Needle No. 2. 



Dip = 71° 15'-93 

 Dip = 71" 14'-87 

 Dip = 71° 16'-96 

 Dip = 71° 16'-27 



115. The dip resulting from these observations differing to a considerable extent from 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 shewn in the 

 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 tlie dip-liouse, the top of the wall being on a level witli the 

 surface of the ground. The following then are the means of all the observations of magnetic dip made with 

 the Makerstoun inclinometer; 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 



Position of 



Mean of 







Observations. 



Inclinometer. 



Observed Dips. 



July —Dec. 1841 



1841-8 



27 



Observatory j 

 Dip-PUlar | 



71 25-90 



Jan. —Dec. 1842 



1842-5 



86 



23-95 



Jan. — June 1843 



1843-2 



36 



22-14 



June— Dec. 1843 



1843-7 



48 





20-20 



Jan.— Dec. 1844 



1844-5 



67 



Dip-house J 



23-69 



Jan.— Dec. 1845 



1845-5 



82 



23-10 



Jan.— Feb. 1846 



1846-1 



12 





22-40 



Oct. 1849 



1849-7 



4 



Observatory ) 

 Dip-PUlar j 



16-00 



116. The observations made in the years 1841-2-3 on the Observatory dip-pillar, give for the mean epoch 

 1842-5, the mean dip = 71° 24'-0 ; those made on the same pillar 1849-7, give the mean dip = 71° 16'-0; 

 whence the change in 7'2 years = — 8'-0, or = — I'll a year. 



