xxu 



Genekal Results or the Makeestoun Observations. 



Table 13. — Diurnal Variations of Westerly Declination for different periods deduced from 



Table 12. 



Mak. 

 Mean 

 Time. 



Dec. 

 Jan. 

 Feb. 



March. 

 April. 



May. 

 June. 



July. 

 Aug. 



Sept. 

 Oct. 

 Nov. 



Six Months. 



Twelve 



Months. 



Sept. to 

 Feb. 



March 

 to Aug. 



h. 



m. 



, 



> 



/ 



' 



/ 



/ 



/ 



, 



12 



10 



-1-78 



-1-92 



-1-73 



-1-90 



-216 



-1-97 



-1-85 



-1-91 



13 



10 



-1-38 



-210 



-1-69 



-2-08 



-2-00 



-1-69 



-1-96 



-1-82 



14 



10 



-1-05 



-206 



-1-62 



-1-97 



-1-40 



-1-22 



-1-88 



-1-55 



15 



10 



-0-77 



-2-34 



-1-93 



-1-78 



-1-40 



-108 



-202 



— 1-55 



16 



10 



-0-70 



-1-84 



-2-83 



-2-77 



-1-37 



-103 



-2-48 



-1-75 



17 



10 



-0-80 



-2-03 



-3-84 



-3-45 



-113 



-0-96 



-311 



-203 



18 



10 



-0-26 



-204 



-4-67 



-3-72 



-0-72 



-0-49 



-3-48 



-1-98 



19 



10 



-013 



-2-53 



-4-62 



-3-78 



-0-77 



-0-45 



-3-64 



-204 



20 



10 



+ 003 



-2-65 



-3-56 



-2-70 



-0-57 



-0-27 



-2-97 



-1-62 



21 



10 



+ 0-44 



-1-45 



-1-76 



-Ml 



+ 0-36 



+ 0-40 



-1-44 



-0-52 



22 



10 



+ 1-45 



+ 0-69 



+ 0-96 



+ 1-37 



+ 2-40 



+ 1-92 



+ 1-01 



+ 1-46 



23 



10 



+ 2-72 



+ 3-75 



+ 3-98 



+ 4-27 



+ 4-50 



+ 3-61 



+ 400 



+ 3-80 







10 



+ 3-47 



+ 6-29 



+ 5-80 



+ 6-30 



+ 5-75 



+ 4-61 



+ 613 



+ 5-37 



1 



10 



+ 3-67 



+ 7-28 



+ 6-53 



+ 6-87 



+ 5-48 



+ 4-57 



+ 6-89 



+ 5-73 



2 



10 



+ 2-90 



+ 6-17 



+ 5-97 



+ 5-93 



+ 4-46 



+ 3-68 



+ 6-02 



+ 4-85 



3 



10 



+ 1-75 



+ 4-46 



+ 4-45 



+ 4-16 



+ 2-71 



+ 2-23 



+ 4-36 



+ 3-29 



4 



10 



+ M1 



+ 2-67 



+ 2-83 



+ 2-52 



+ 1-00 



+ 1-05 



+ 2-67 



+ 1-86 



5 



10 



+ 0-26 



+ 0-30 



+ 1-27 



+ 1-09 



+ 003 



+ 0-14 



+ 0-89 



+ 0-51 



6 



10 



-0-61 



-0-94 



+ 0-47 



-0-34 



-1-24 



-0-92 



-0-27 



-0-59 



■7 



10 



-1-05 



-1-43 



-005 



-0-66 



-1-93 



-1-49 



-0-71 



-110 



8 



10 



-215 



-1-84 



-0-61 



-0-96 



-305 



-2-60 



-114 



-1-87 



9 



10 



-2-36 



-211 



-0-81 



-1-67 



-2-89 



-2-62 



-1-53 



-207 



10 



10 



-2-46 



-1-99 



-102 



-1-87 



-3-01 



-2-73 



-1-63 



-2-18 



11 



10 



-2-36 



-2-45 



- 1-55 



-1-79 



-301 



-2-68 



-1-93 



-2-30 



time 



32. The following are the epochs of maximum and minimum westerly declination from Table 1 3 in apparent 



Dec. Jan. Feb. 

 Max. O'' 50m P.M. 

 Min. 8^ P.M. — ll'^ P.M. 



Mar. April. 

 1*> 5"^ P.M. 

 8'' Om A.M. 



May. June. 



P 15"! P.M. 

 e'^ 30m _^,M. 



July. Aug. 

 Oh 50°> P.M. 

 6b 40m A.M. 



Sept. Oct. Nov. 



0'' 35m p M. 



B*' P.M. 11'' P.M. 



33. The form of the diurnal curve is the same for each of the periods of three months ; the westerly decbna- 

 tion decreases regularly from the maximum till about 8'^ p.m., whereas in the curves for the summer months, 

 the rate of decrease receives a check about 5'' or %^ p.m. (see Plate I.) No secondaiy maximum or minimum 

 is shewn in these means, but the magnet is nearly stationary for several hours in each case, namely from 

 8^ to ll'' p.m. in the months from September to February ; from S** p.m. till 6"'' a.m. in the mean for March 

 and April, from midnight till 3*^ a.m. in May and June ; and from 9** p.m. till S*" a.m. in June and July. The 

 magnet is stationary for nearly twelve hours about the 23d of March : the transposition of the minimum of 

 westerly declination from before midnight till about 8'^ a.m. takes place very gxadually in March and Api-il ; 

 this does not appear to be the case, however, in the return of the minimum from 7'' a.m. to before midnight, 

 which occurs about three weeks before the autumnal equinox. 



34. When we examine the diurnal curve deduced from the observations for the whole year (Plate I.), we ob- 

 serve a secondary maximum of westerly declination occurring at 2'^ 40™ a.m., nearly equal minima occuning at 

 11'' P.M. and 6^ a.m. ; this secondary maximum is evidently due to the occurrence of the minimum for one- 

 half of tKe year about 10'' p.m., and for the other half about 7^ a.m. ; The mean for the year therefore does not 

 represent, as far as these results are concerned, a real phenomenon ; it is a combination of two distinct results. 



35. The previous conclusions are obtained from the means of all the regular daily observations ; no observa- 

 tion has been rejected how ever much affected by magnetic irregularity ; we have still to inquire therefore to 

 what extent irregular causes change the diurnal variation. A method has been already proposed and employed 



