388 Results of Makeestoun Obseevations, 1844. 



minimum is but slightly less than the secondary minimum. The mean difference has nearly a constant value 

 from midnight till 5 h a.m. The following are the approximate times of maximum and minimum for each of 

 the astronomical quarters of the year ; the principal maximum, when it is distinctly marked, is indicated by + , 

 and the principal minimum by — 



Nov., Dec, Jan., . Min.-10 h A.M. Max. + 5 h 30 m p.m. Min. 9 h p.m. Max. 12 h 10 m a.m. 



Feb., March, April, -10 a.m. 6 10 p.m. 8 30 p.m. + 2 30 a.m. 



May, June, July, — 2 p.m. 5 10 p.m. 9 30 p.m. +1 10 a.m. 



Aug., Sept. Oct., . — 9 a.m. 5 10 p.m. 9 p.m. +5 a.m. 



Year, . -10 a.m. + 5 20 p.m. 8 50 p.m. 2 30 a.m. 



The law of variation of the diurnal disturbance of the vertical component has a considerable constancy in 

 each quarter of the year ; the differences are even less considerable than appears from the foregoing Table of epochs 

 of maxima and minima. 



Annual Variation of the number of Positive Differences. — The following are the numbers of differences in 

 100, which are positive for each month: — 



Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



53-0 



49-5 



57-7 



49-8 



52-5 



55-7 



55-4 



52-0 



55-0 



50-0 



46-5 



40-7 



These quantities do not vary regularly ; on the whole, the vertical component was oftenest in excess of the 

 monthly mean for the corresponding hours in the months from March till September, and least often in excess 

 in the months of November and December. There were about 52 positive to 48 negative differences in the year 

 1844, 



Diurnal Variation of the number of Positive Differences. — The numbers of positive differences in 100 for 

 each hour of Makerstoun mean time in 1844, are as follow : — 



12 h lhA.M. 2 l1 3 h 4 h 5 h G h 7 h 8'> 9 h 10 h 11^ h l h P.M. 2 h 3 h 4 h 5>» fi h 7' 1 8 h 9 h 10 h ll 1 ' 



65-2 63-3 66-5 63-9 63-9 639 63-0 54-6 52-7 52-7 52-1 47-6 40-9 42-8 409 37-1 36-7 351 37-7 37-1 45-7 54-0 569 61-3 



The number of positive differences is greatest about 2 h a.m., and is least about 5 h p.m. These are the 

 epochs already obtained for the greatest negative and positive effects of disturbance on the vertical component 

 (see p. 384). 



Mean Disturbance. 



Deducing the differences by using the means obtained from the 5 days least disturbed, Table XLV., 

 in the manner already done for the declination, pages 349 and 350, we obtain the following results : — 



Annual Variation of the Mean Disturbance. — The following are the mean disturbances, in micrometer 

 divisions, for a single observation of the vertical component in each month of 1844 : — 



Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



12-3 



15-9 



27-8 



23-1 



21-1 



14-5 



13-8 



17-9 



18-5 



23-7 



18-7 



12-1 



These quantities differ little from the mean differences, page 385, and they follow the same law. The 

 disturbance of the vertical component is a maximum near the equinoxes, and a minimum near the solstices. 

 The mean disturbance of an observation of the vertical component for the year 1844 = 18*3 Mic. div. 



Diurnal Variation of the Positive and Negative Sums of Disturbance. — The following are the sums of the 

 positive and of the negative disturbances, in micrometer divisions, for each hour of the day in 1844 : — 



12 h lhA.M. 2 h 3 h 4 h 5 h 6'> 7 h 8 h 9 h 10 h ]l h 0>> Jtp.M. 2 h 3 h 4 h 5>> C' 1 7 h 8 h 9 h 10 h ll h 

 +1169 1330 1132 1193 1235 1323 1308 1398 1259 1536 1843 2560 3413 3552 3998 5262 6002 6974 6926 5672 4142 2683 1G35 1297 

 -5764 5614 5774 5636 5508 5260 4604 3383 2931 2369 1838 1512 1289 1164 1226 1048 1010 806 858 817 1018 1926 3342 4125 



The sums of the positive disturbances — those which increase the value of the vertical component — are a 

 maximum at 5 h 30 m p.m., and they are a minimum from ll h p.m. till 8 h a.m.; during which interval, the 

 positive disturbance has nearly a constant value. The sums of the negative disturbances are a minimum 



