Magnetic Declination. 



225 



TABLE IV. — Diurnal Variation of Westerly Declination for each Month in 1843. 



Period. 



ISi. 



201'. 



22ii. 



23i>. 



Oh. 



2". 



4h. 



6". 



gi. 



10i>. 



Range. 



January 



0-26 



0-93 



0-55 



/ 



3-47 



4-92 



1 

 3-10 



1-82 



/ 

 1-01 



0-00 



4-92 



February 



2-88 



3-15 



3-65 





6-78 



8-35 



6-59 



4-86 



2-91 



0-00 



8-35 



March 



0-80 



1-29 



0-98 





5-30 



7-93 



6-67 



3-29 



2-20 



0-00 



7-93 



April 



0-69 



0-00 



211 





711 



10-52 



7-70 



3-39 



1-65 



0-78 



10-52 



May 



0-97 



0-00 



2-16 





7-26 



9-93 



7-26 



4-76 



3-84 



2-75 



9-93 



June 



1-13 



0-00 



2-83 





8-35 



11-14 



8-96 



5-59 



4-78 



4-44 



11-14 



July 



0-35 



000 



2-08 





7-08 



9-95 



7-62 



5-06 



3-39 



1-33 



9-95 



August 



1-32 



0-00 



3-29 





8-41 



10-83 



7-67 



3-99 



2-67 



2-78 



10-83 



September 



2-72 



2-79 



3-98 





9-06 



10-75 



8-18 



4-53 



2-22 



0-00 



10-75 



October 



2-20 



2-69 



3-07 





7-60 



7-90 



5-37 



3-13 



1-89 



0-00 



7-90 



November 



M2 



1-37 



1-54 



2-94 



4-59 



4-63 



3-56 



2-33 



0-50 



0-00 



4-63 



December 



2-31 



2-33 



2-87 



3-84 



4-88 



5-73 



4-36 



3-04 



0-58 



0-00 



5-73 



Spring 



1-20 



1-22 



1-99 





6-14 



8-67 



6-73 



3-59 



1-99 



0-00 



8-67 



Summer 



0-82 



0-00 



2-36 





7-56 



10-34 



7-95 



5-14 



4-00 



2-84 



10-34 



Autumn 



M5 



0-90 



2-52 





7-43 



8-90 



6-14 



2-95 



1-33 



0-00 



8-90 



Winter 



1-23 



1-54 



1-65 





4-31 



5-09 



3-67 



2-40 



0-70 



0-00 



5-09 



The Year 



0-39 



0-20 



1-42 





5-64 



7-54 



5-41 



2-80 



1-29 



0-00 



7-54 



Table IV. has been obtained from Table III. in subtracting the lowest mean in each month from all the other 

 means. Spring in the above Table consists of the months of February, March, and April. 



Diurnal Variation of Declination. 



The least westerly declination occurs in the first three and last four months of the year, at or after 9^^ lO'" p.m. 

 Makerstoun mean time ; in the remaining five months at 1^ 10™ a.m. Mak. The greatest westerly declination 

 occurs in each month at 1"^ 10™ P.M., but in the winter months the maximum probably occurs before this time. 

 The westerly declination increases with more rapidity to the maximum at l** 10™ p.m. than it diminishes after it, 

 and in nine months the rapidity of diminution is less after 5"^ 10™ p.m. than before it. In the winter months, the 

 westerly declination does not begin to increase rapidly till %^ 10™ a.m., whereas in summer, it does so at 7*^ 10™ a.m. 

 While this fact seems to shew some relation to sunrise, there is no corresponding one to sunset, but rather the 

 reverse ; for in winter the westerly declination diminishes with nearly equal rapidity from the maximum at 

 jh j^q™ p.m. till 9^ 10™ p.m., whereas in summer, on the whole, the rate of diminution seems to receive a check 

 about 5^ 10™ P.M. 



The minimum of westerly declination occurs in spring, autumn, and winter at or after 9** 10™ p.m.; in 

 spring and autumn a secondary minimum also occurs about G^ 10™ a.m. In summer the principal minimum 

 occurs at 1^ 10™ a.m. The principal maximum occurs about O'' 40™ p.m. in winter, and about 1^ 10™ p.m. in summer. 



In the mean for the year 



The maximum of westerly declination occurs about l** 



The minimum after 9 



A minimum about 7 



0™ p.m. Makerstoun mean time. 



10 P.M. 



A.M. 



The exact periods of the principal minimum, and of the secondary maximum, cannot be determined from these 

 observations; they are found, however, from the Term-day Observations in the years 1842 and 1843. The fol- 

 lowing Table contains the results of the summations of the observations at 0™ on 11 Term-days of 1 842 (January 

 Term-day being rejected), and on 11 Term-days of 1843 (June Term-day being rejected). 



MAG. AND MET. OBS. 1843. 



3l 



