XXxil GENERAL RESULTS OF THE MAKERSTOUN OBSERVATIONS. 
TABLE 13.—Diurnal Variations of Westerly Declination for different periods deduced from 
Table 12. 
Six Months. 
—_—___—_—_——| Twelve 
Sept. to March Months. 
Feb. 
KH OCOODNHWAUHPWNWH OS S 
— 
32. The following are the epochs of maximum and minimum westerly declination from Table 13 in apparent 
time: 
Dec. Jan. Feb. Mar. April. May. June. July. Aug. Sept. Oct. Nov. 
Max. 0 50™p.m. 15 5™ p.m. 1» 15™ p.m. 0» 50™ pM. 0b 35™ p.m. 
Min. 8" p.w.—11 p.m. 8h Om a.m. 65 30™ a.m. 6> 40™ a.m. 8" 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 declina- 
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 6" p.m. (see Plate I.) No secondary maximum or minimum 
is shewn in these means, but the magnet is nearly stationary for several hours in each case, namely from 
85 to 11" p.w. in the months from September to February ; from 8» p.m. till 64 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 3" 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 gradually in March and April ; 
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 oceurring at 
11" p.m. and 6" a.m.; this secondary maximum is evidently due to the occurrence of the minimum for one- 
half of the year about 10 p.m., and for the other half about 74 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 
