1 



XXVIU 



General Results of the Makeestoun Observations. 



1st, The average westerly excursion from the mean position for the hour is greatest in the winter and 

 spring quarters about 1'^ or 2^ p.m. ; and about 8^ a.m. in the summer and autumn quarters, although the 

 values vary little in the summer quarter from 4^ a.m. to 1'' p.m., and in the autumn quarter a secondarv 

 maximum occurs at 3*^ p.m. 



2d, The average easterly excursion is least about 8^ a.m. in each quarter, with the exception of summer, 

 in which it is equally small at 5'' p.m. : the average easterly excursion from the hourly mean of all the obser- 

 vations (Table 18) has the minimum decidedly marked at 6^ p.m. 



3d, The minimum westerly excursion occurs about 9^ p.m. in all the quarters. 



4th, The maximum easterly excursion occurs earliest in winter, about 6^ p.m., and latest in summer, 

 namely after midnight ; while in the equinoctial quarters it occurs betwixt these epochs, the values varying 

 little from 6^ p.m. till midnight. 



5th^ The mean excursion, without reference to direction, has its greatest value earliest in winter, about 

 6^ p.m. ; about 9^^ and 10*^ p.m. in the equinoctial quarters ; and in summer there are two maxima of nearly 

 equal value, immediately after midnight and at 11^ a.m., with a secondary minimum about 6^ a.m. 



6th, The mean excursion has its least value about 5^ to 6^ x m. in winter and spring ; a secondary mini- 

 n)um, as noted above, occurs about the same hour in summer, and 4*^ in autumn ; but the actual minimum 

 occurs, distinctly marked, between 6*^ and lO'^ p.m. in summer, and, less distinctly marked, about 5^ p.m. in 

 autumn. 



45. It appears from these results, that the diurnal law of mean distui'bance is not constant throughout the 

 year, as has been supposed ; in fact the law for summer is nearly the reverse of that for winter, while that for 

 autumn is nearly intermediate between the two, a secondary maximum occurring in the latter at 9*^ a.m. In 

 the winter and spring quarters there is a tendency to a secondary minimum about 4'' or b^ p.m. 



Table 19. — Mean Disturbances of Magnetic Declination, or DiiFerences from the Monthly Means, at 

 the corresponding Hours in 1844 and 1845, as deduced from the selected series in each Year. 



Mak. 



Mean 



Mean Westerly Disturbance. 



Mean Easterly D 



isturbance. 





Mean Disturbances. 





Nov. 



Feb. 



May. 



Aug. 





Nov. 



Feb. 



May. 



Aug. 





Nov. 



Feb. 



May. 



Aug. 





Time. 



Dec. 



Mar. 



.June. 



Sept. 



Year. 



Dec. 



Mar. 



June. 



Sept. 



Year. 



Dec. 



Mar. 



June. 



Sept. 



Year. 





Jan. 



April. July. 



Oct. 





Jan. 



April. 



July. 



Oct. 





Jan. 



April. 



July. 



Oct. 



I 



h. m. 



12 10 



0-96 



1-47 



102 



156 



1-25 



2-26 



2-88 



202 



2^50 



2-40 



1-74 



2^22 



1-66 



2-21 



I 



195 



13 10 





00 



\A1 



117 



1-68 



1-32 



2-45 



2-94 



L98 



2-29 



2-33 



1-82 



2-22 



\-m 



2-10 



194 



14 10 





•23 



1-56 



1-09 



1-85 



1-44 



1-84 



2^69 



181 



2-34 



2-15 



1-56 



2-12 



152 



214 



183 



15 10 





•25 



1-43 



150 



2^09 



1-54 



1-92 



212 



1^44 



1^96 



1-85 



1-56 



1^77 



L47 



201 



170 



16 10 





■37 



177 1-92 



L86 



171 



1-38 



1-84 



].34 



b53 



151 



1-38 



181 



155 



166 



1-60 



17 10 





■ 18 



b56 L82 



2-37 



171 



M4 



1-24 



M8 



1-29 



1-21 



M6 



L39 



1^46 



L80 



145 



18 10 





53 



L39 



L74 



2-57 



1-79 



0-82 



1-08 



M8 



0-93 



bOl 



1-24 



1^29 



146 



1-85 



1^46 



19 10 





■57 



1-55 



1-72 



2-52 



1-83 



0-64 



0-80 



M2 



0-93 



0-90 



b26 



1-29 



1-41 



1-86 



1-46 



20 10 





■74 



1^83 



1-92 



2-77 



2-07 



0-59 



0-86 



0-92 



0-63 



0-76 



1-37 



1-43 



L48 



196 



156 



21 10 





•92 



1-83 



1-94 



273 



209 



0-69 



0^95 



Ml 



0-95 



0-93 



1-58 



1-57 



1-65 



204 



1-71 



22 10 





•76 



1-78 



L88 



2^23 



1-90 



0-87 



0^84 



1-08 



Ml 



0-99 



h50 



1-45 



1-64 



1-76 



1-59 



23 10 





•78 



1-66 



1^98 



1-96 



L85 



0-84 



0-95 



1-26 



1-00 



102 



142 



h39 



171 



164 



1^54 



10 



2 



17 



1-84 



1-68 



1-83 



1-89 



0-86 



114 



1-27 



106 



1-08 



1^75 



i-m 



1^54 



159 



162 



1 10 



2 



27 



b84 



1-92 



b90 



1-98 



0-98 



1-03 



M8 



1-38 



M4 



1-80 



1-58 



1-62 



1^72 



1-68 



2 10 



2 



16 



1-98 



1-73 



210 



1-99 



0-90 



1-08 



Ml 



b26 



b09 



1-72 



1-67 



1-50 



1-80 



1-67 



3 10 



1 



98 



1^82 



L61 



2-27 



1^91 



1-63 



1^36 



131 



1-42 



r42 



1^86 



1-67 



1-49 



1^88 



172 



4 10 



1 



88 



151 



1-41 



174 



1-63 



1-60 



1-58 



1-23 



1-27 



139 



\-7S 



1-53 



1-34 



1-53 



1-54 



5 10 



1 



34 



r43 



M4 



\AS 



1-36 



1-85 



2-23 



097 



1-36 



155 



1^55 



1-81 



1-04 



1^42 



145 



6 10 



1 



37 



MO 



0^82 



M4 



M3 



3-52 



3-03 



1-09 



2-72 



2-49 



2-27 



2-09 



0-98 



1-87 



1-80 



7 10 







99 



M5 



0-72 



0^95 



0^96 



2-67 



275 



1-37 



2-43 



2-26 



1-85 



2-00 



112 



1-69 



1-66 



8 10 







82 



105 



0-58 



0^91 



0-86 



3-08 



2-77 



b48 



2^96 



2-54 



2-22 



200 



117 



2^17 



1-89 



9 10 







70 



1-35 



0-51 



0-77 { 



0-83 



3-33 



3^13 



1^43 



3-03 



269 



\-90 



2-34 



106 



2-26 



1-89 



10 10 







99 



M4 



0-62 



L07 



0-95 



2-84 



2-80 



1-29 



2-77 



2-43 

 2-63 



2-11 



2-06 



103 



2^28 



1^87 



11 10 



0- 



71 



100 



0-64 



105 



0^86 



2-95 



2-94 



1-70 



3-02 



2-13 



203 



1-33 



2-21 



192 



46. Diurnal Variation of the probable error of an Observation of Magnetic Declination. — It appears from 

 the previous conclusions, that the best hour to make an observation of magnetic declination in winter and 

 spring, is about G*" a.m. ; in the summer quarter, from b^ p.m. to lO'' p.m. ; and in autumn fi-om 4*^ to 5^ p.m. 



