390 



Results of Makerstoun Observations, 1844. 



The probable error of an observation of the vertical component from the monthly mean for the 



,. , .,, ,, „ , . f December and February about O00008 1 « ,, . . 



corresponding hour will therefore be in , l T 1 0-00010 I whole component. 



These values are estimated from a consideration of the results for the declination, p. 352. 



The mean difference of an observation is least at 10 h a.m., being 11*6 micrometer divisions, when the 

 mean for the whole year is considered. The probable error of an observation from the monthly mean for the 

 corresponding hour, without reference to which month, will be less than 0-00008 of the whole vertical 

 component. 



Magnetic Dip. 



The following results are deduced from the variations of the horizontal and vertical components of mag- 

 netic force by means of the formula 



i sin 2 / A Y A X \ 



\~y xV 



A 6 = 



0-0002909 



where -=r- and -^r- are the variations respectively of the vertical and horizontal components, as given in the 



previous Tables, 6 is the magnetic dip, assumed to be 71° 18', A is the variation of dip, as given in the follow- 

 ing Tables, and 0-0002909 is the value of 1' in parts of radius. 



Secular Change of Magnetic Dip. — This deduced froin the mean secular changes for the two components, 

 pages 356 and 374, = — 6'-l. It is very probable that this change is considerably too great, and therefore 

 that the secular change for one or both components is also in error, or is due to instrumental causes. 



Annual Period of Magnetic Dip. — The following monthly means are obtained from the means for the two 

 components, pages 356 and 374, where the secular change is eliminated : — 



Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



0'-95 



0'-76 



l'-23 



l'-35 



0'-68 



0'-07 



O'-OO 



0'-39 



0'-73 



l'-00 



r-oi 



0'-76 



From these quantities the magnetic dip appears to be a maximum about the beginning of April and the 

 beginning of November ; it is a principal minimum about the beginning of July, and a secondary minimum 

 about January. This result differs somewhat from the result obtained from the observations for 1843 (p. 248) ; 

 this is obviously due to the difference in the results for the vertical component in the two years. 



TABLE LIV. — Variations of Magnetic Dip with reference to the Moon's Age, Declination, and Dis- 

 tance, as deduced from Tables XXIII. and XXXIX. 





Variations 





Variations 



After 



Variations 



.After 



Variations 



Before 



Variations 



Before 



Variations 



Moon's 



of 



Moon's 



of 



Moon 



of 



Moon 



of 



and 



of 



and 



of 



Age. 



Magnetic 



Age. 



Magnetic 



farthest 



Magnetic 



farthest 



Magnetic 



after 



Magnetic 



after 



Magnetic 





Dip. 





Dip. 



North. 



Dip. 



North. 



Dip. 



Perigee. 



Dip. 



Apogee. 



Dip. 



Day. 



> 



Day. 



• 



Day. 



' 



Day. 



' 



Dav. 



> 



Dav. 



' 



15 



0-411 



6 



0055 



6 



0-138 



14 



0-155 



7 



0-278 



7 



0176 



16 



0-410 



1 



0133 



1 



0-113 



15 



0045 



6 



0-330 



6 



0-182 



17 



0-597 



2 



0-077 



2 



0000 



16 



0043 



5 



0-404 



5 



0-338 



18 



0-505 



3 



0098 



3 



0-194 



17 



0-169 



4 



0-335 



4 



0-401 



19 



0-589 



4 



0-000 



4 



0-305 



18 



0-198 



3 



0-273 



3 



0-361 



20 



0-469 



5 



0-072 



5 



0-480 



19 



0-215 



2 



0-251 



2 



0-433 



21 



0-370 



6 



0-147 



6 



0-421 



20 



0-270 



1 



0-248 



1 



0-382 



22 



0-323 



7 



0-152 



7 



0-423 



21 



0-405 



P 



0096 



A 



0-306 



23 



0-388 



8 



0-133 



8 



0-326 



22 



0-350 



1 



0-077 



1 



0-231 



24 



0-233 



9 



0-428 



9 



0-333 



23 



0-412 



2 



0-167 



2 



0-069 



25 



0133 



10 



0-511 



10 



0-298 



24 



0-543 



3 



0-181 



3 



0000 



26 



0-157 



11 



0-491 



11 



0-114 



25 



0-398 



4 



0071 



4 



0-024 



27 



0-027 



12 



0-575 



12 



0-144 



26 



0-464 



5 



0-187 



5 



0-060 



28 



0-025 



13 



0-466 



13 



0-130 



27 



0-277 



6 



0042 



6 



0-291 



29 



0-003 



14 



0-547 











7 



0-274 



7 



0-421 



