394 Results of Makeestoun Observations, 1844. 



Intermittent Disturbances. 

 Effect of Intermittent Disturbances wpon the Yearly Mean of Magnetic Dip. — We obtain the following 

 results for the mean magnetic dip from the values of the horizontal and vertical components, pages 365 and 384 : — 



The Mean Magnetic Dip, as deduced from the whole series of Hourly "1 120-day series, by 0'-175 

 Observations, is greater than that deduced from the J 60-day series, by 0'-245 



It has been foimd, p. 343, that the intermittent disturbances have no eftect on the mean declination ; it ap- 

 pears, however, from the above results, that they affect the mean dip, the result deduced from the 60-day series, 

 that least aftected by disturbance, shewing a less dip tliau that deduced from the whole series, by 0'-25, which 

 is equivalent to about 0'-8 for the magnetic declination. 



Effect on the Monthly Mean of Magnetic Dip. — ^Making use of the quantities for the two components offeree, 

 pages 365 and 384, we obtain the following corrections of the means of magnetic dip from the 10-day and 5-day 

 series, to those from the complete series of observations in each month : — 



Jan. Feb. Jlarch. April. JIay. June. July. Aug. Sept. Oct. Nov. Dec. 



10 days -i-0'-07 +0'-46 -i-0'-29 -|-0'-33 -0'-04 -0'-05 -O'Ol +0'-09 +0'-01 +0'-48 4 0'-18 -f-0'-30 

 5 days', +0'-13 -t-0'-54 -i-0'-42 +0'-42 + O'-IO -0''23 -0'-03 +0'-14 -l-0'-13 -i-0'-56 + 0'-36 -t-0'-38 



These quantities obey the same law as that deduced from the mean variations of dip for each month ; upon 

 applyino- them with an opposite sign, as corrections to the mean variations of dip, p. 390, we obtain the follow- 

 in" monthly mean variations of magnetic dip, as deduced from tlie 10-day and 5-day series of observations 

 selected in each month as least affected by disturbance : — 



Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 



10 days, 0'-88 0'-30 0'-94 l'-02 0'-72 0'-12 O'Ol 0'-30 0'-71 0'-52 0'-83 0'-46 

 5 days, 0'-82 0'-22 0'-81 0'-94 0'-58 0'-30 0'03 0'-25 0'-60 0'-44 0'-65 0'-38 



The variations follow the same law, with some irregularities, as the variations from the complete series ; 

 the rano-es, however, are smaller ; the conclusion already stated, with respect to the horizontal component, is 

 therefore equally applicable here, see p. 356. 



Effect of Disturbances on the Hourly Means of Magnetic Z>(p.— The following are the differences of the 

 hourlv means of magnetic dip for the year, or the means as deduced from the whole series, minus the means as 

 deduced from the 120-day and 60-day series of observations (see Table LV. and p. 392), each series having 

 the same mean value. 



^^'"S/Lm""' a.m.1211 Hi 2b Sl> 41> 61i eh 71. 8h Oh lOh Ub 



120-day scries, -0'05 -0-01 +0'03 -0-0.5 -0-08 -010 -0-16 -0-05 -0-01 +0-03 4-0-06 +0-03 

 60-day series, -HO-01 +0-05 -hO-08 -0-01 -0-07 -0-10 -0-17 -0-05 -0-03 +0-02 +0-07 -0-02 



P.M. Ob lb 2h 3b 4h .-jh Ch 7b 8b Ob lOh lib 



120-day series, -0-08 -0-03 -0-07 0-00 -0-10 -0-07 +0-06 +0-13 +0-03 +0-18 +0-12 +016 



60-day series, -0-09 -0-05 -0-09 -0-06 -0-15 -0-04 +0-06 +0-12 +0-08 +0-22 +0-08 +0-14 



Both series of differences give the same law ; considering the differences for the 60-day series, we find that 

 the mean effect of disturbance upon the diurnal variation of magnetic dip is a positive maximum twice and a nega- 

 tive maximum twice ; it is a principal positive ma.ximum about 9'' p.m. and a secondary positive maximum at 

 lO"" A.M. : it is a negative maximum at 6'' a.m. and about o'" p.m. The effect of disturbance in diminishing the 

 westerly declination, and in increasing the dip, is a maxinmni about 9'' p.m. ; the effect of disturbances in in- 

 creasino- the westerly declination is a maximum about 10'' a.m., when their effect in increasing the dip is a 

 secondarv maximum. The effect of disturbances in diminishing tlie dip is a maximum when the effect upon the 

 magnetic declination is zero. 



Total Magnetic Force. 



The following results are deduced from the variations of the horizontal and vertical components by means 

 of the formula 



aE, aY ., ./"^Y aX\ 



= cos-dl 1 



R Y V Y X ^ 



where ^- is the variation of the total force, —.^ and —— the quantities in the tables for the vertical 

 and horizontal components respectively, and i the magnetic dip assumed = 71° 18'. 



t 



