Ixiv 



General Results of the Makerstoun Observations. 



131. Diurnal Variation of the Effect of Disturbance on the Magnetic Dip. — A remark, similar to that 

 made No. 72, with reference to the horizontal component, will apply to Table 60. The conclusions from this 

 Table are as follow : — 



\st, The greatest effect of disturbance in increasing the magnetic dip occurs 



In Dec. Jan. Feb. March, April. May, Jane. 



P.M. and Sl^'^ A.M. 



About 



12^1^ A.M. 



A.M. 



March, April. 

 l^^ A.M. 

 8*1' A.M. 



11» 



July, Aug. 



Sept. Oct Nov 



Q^ A.M. 



^^ P.M. 



^^ P.M. 



10" P.M. 



There are two epochs in May and June at which the positive effect of disturbance is a maximum, and there 

 are two similar epochs for each group of months, for one of which either the positive effect is a secondary maxi- 

 mum, or the negative effect is a minimum ; the times of these are given above, in the second line. 

 2d, The greatest effect of disturbance in diminishing the magnetic dip occurs 



In 



Dec. Jan. Feb. 



About { &" A.M. and Z^ p.m. 



March, April. 

 4'" P.M. 

 &" A.M. 



May, June. 

 4'' P.M. 

 4'' A.M. 



July, Aug. 



b^ P.M. 

 12^ P.M. 



H' 



Sept. Oct. Xov. 

 A.M. and ^^ PM. 



In the winter groups there are two nearly equal maxima for the negative effect of disturbance, and in each of 

 the others there is, besides the principal maximum, either a secondary maximum of the negative effect, or a 

 minimum of the positive effect ; the times of these are given above in the second line. 

 'id, The effect of disturbance upon the hourly mean magnetic dip is zero 



In Dec. Jan. Feb. 



About lOl" A.M., 1^ P.M., Z^ A.M. 



March, April. 

 A.M., lO"" A.M., 1^ P.M. 



May, June. 

 Noon, 9'' P.M. 



.luly, Aug. 

 \^ P.M., S"" P.M. 



Sept. Oct. Nov. 

 10'' A.M., e"" P.M., Ih A.M. 



The best defined hours are those from 6'' p.m. to 9^ p.m., and from IQ^ a.m. to l** p.m. 



See No. 76 for the probable law of mean disturbance for the magnetic dip, substituting for positive distur- 

 bance of the horizontal component, negative disturbance of dip, and vice versa. 



Table 61. — .Variations of the Magnetic Dip with reference to the Moon's Hour- Angle for the Winter 

 and Summer Lunations, and for all the Lunations of the Years 1844 and 1845. 



Moon's 

 Hour- 



Wi 



nter Lunations. 



Summer Lunations. 



All the Lunations. 





















Angle. 



1844. 



1845. 



Mean. 



1844. 



1845. 



Mean. 



1844. 



1845. 



Mean. 



h. m. 







-1--012 



+ •021 



+ •017 



-■012 



-•045 



-■028 



•000 



-009 



-005 



2 25 



-h.048 



-123 



-037 



-031 



-•154 



-092 



+ •009 



-•138 



-•063 



4 20 



-•010 



+ 071 



+ •030 



-033 



-•071 



-■051 



-022 



+ ■004 



-•008 



6 15 



-026 



+ •018 



-•004 



+ ■006 



+ •006 



+ ■006 



-009 



+ •012 



+ •001 



8 10 



-•064 



+ •084 



+ •010 



+ ■030 



+ •170 



+ ■100 



-•018 



+ •123 



+ •052 



10 5 



! +^030 



+ •024 



+ •027 



+ .003 



-031 



-■014 



+ •016 



-•002 



+ •007 



12 



-066 



+ •001 



-•031 



-■108 



-096 



-■101 



-•087 



-•044 



-•066 



13 55 



-t-^OOS 



-•037 



-•015 



-156 



-•075 



-•115 



-•073 



-•055 



-•063 



15 50 



-h099 



-•090 



+ •004 



+ ■009 



+ •042 



+ •026 



+ •055 



-•030 



+ •012 



17 45 



-■046 



-■027 



-•036 



+ •073 



+ •085 



+ •080 



+ •020 



+ •024 



+ 021 



19 40 



-•023 



+ 011 



-■006 



+ •138 



+ ■106 



+ •123 



+ •058 



+ •054 



+ •056 



21 35 



+ •025 



+ •058 



+ •042 



+ •074 



+ 057 



+ •066 



+ •052 



+ •057 



+ 055 



132. Variations of the Magnetic Dip vnth Reference to the 3Ioons Hour-Angle. — The four independent 

 columns of Table 61, give results quite analogous to those obtained for the horizontal component of magnetic 

 force. No. 79 : the results for the winter lunations of 1844, and for the summer lunations of both years, agree 

 very nearly with that for the mean of both years in the last column of Table 61, — which may be stated as 

 follows : — 



The magnetic dip is a minimum about 1 hour after the moons inferior transit. 



maximum about 3|- hours before the moon's superior transit. 



minimum about 2^ hours after the moon's superior transit. 



maximum about 8 hours after the moon's superior transit. 



