Diurnal Variations for the Horizontal Component. 



Xll 



Table 34. — Differences of Disturbed and Undisturbed Diurnal Variations of the Horizontal Com- 

 ponent of Magnetic Force, as deduced from Tables 32 and 33, exhibiting the eflFect of Irregular 

 Disturbance on the Hourly Mean Positions. 



Mak. 

 Mean 



Dec. 

 Jan. 











Six Months. 





March. 



May. 



July. 



Sept. 

 Oct. 



Sept. 

 to 



March 



Twelve 



Time. 



Feb. 



April. 



June. 



Aug. 



Nov. 



to 



Months. 















Feb. 



Aug. 





h. m. 



0-00 



O'OO 



0-00 



0-00 



0-0(1 



0-00 



0-00 



0-00 



12 12 



-0134 



-0221 



-0218 



-0075 



-0196 



-0165 



-0171 



-0169 



1.3 12 



-0092 



-0404 



-0216 



-0189 



-0075 



-0084 



-0270 



-0177 



14 12 



-0277 



-0647 



-0232 



-0226 



-0201 



-0239 



-0368 



-0304 



15 12 



-0108 



-0178 



-0210 



-0227 



-0032 



-0070 



-0205 



-0137 



16 12 



-0003 



-0172 



-0260 



-0240 



-0027 



-0015 



-0224 



-0119 



17 12 



+ 0079 



-0143 



-0164 



-0304 



-0025 



+ 0027 



-0204 



-0087 



18 12 



+ 0113 



+ 0019 



-0136 



-0178 



-0015 



+ 0049 



-0098 



-0025 



19 12 



+ 0063 



-0038 



-0178 



-0201 



-0093 



-0015 



-0139 



-0077 



20 12 



+ 0027 



-0179 



-0240 



-0247 



-0013 



+ 0006 



-0222 



-0108 



21 12 



-0061 



-0143 



-0193 



-0244 



-0082 



-0072 



-0194 



-0134 



22 12 



-0040 



+ 0011 



-0162 



-0181 



+ 0006 



-0017 



-0111 



-0064 



23 12 



+ 0048 



+ 0042 



-0050 



-0083 



-0015 



+ 0016 



-0031 



-0007 



12 



+ 0022 



+ 0138 



+ 0062 



-0018 



+ 0140 



+ 0080 



+ 0061 



+ 0070 



1 12 



+ 0039 



+ 0305 



+ 0145 



+ 0064 



+ 0177 



+ 0107 



+ 0171 



+ 0140 



2 12 



+ 0107 



+ 0360 



+ 0330 



+ 0101 



+ 0199 



+ 0153 



+ 0264 



+ 0209 



3 12 



+ 0166 



+ 0334 



+ 0261 



+ 0310 



+ 0307 



+ 0236 



+ 0302 



+ 0269 



4 12 1 



+ 0136 



+ 0507 



+ 0514 



+ 0558 



+ 0202 



+ 0169 



+ 0526 



+ 0348 



5 12 1 



-0005 



+ 0524 



+ 0430 



+ 0669 



+ 0261 



+ 0128 



+ 0541 



+ 0334 



6 12 



+ 0052 



+ 0325 



+ 0393 



+ 0578 



+ 0112 



+ 0082 



+ 0432 



+ 0257 



7 12 i 



+ 0083 



+ 0054 



+ 0401 



+ 0318 



-0008 



+ 0038 



+ 0258 



+ 0148 



8 12 i 



+ 0075 



+ 0002 



+ 0155 



+ 0102 



-0106 



-0016 



+ 0086 



+ 0036 



9 12 



+ 0043 



-0129 



-0097 



-0093 



-0173 



-0065 



-0107 



-0085 



10 12 



-0175 



-0235 



-0096 



-0063 



-0189 



-0182 



-0131 



-0157 



11 12 



-0152 



-0142 



-0253 



-0122 



-0167 



-0159 



-0173 



-0166 



73. The conclusions from Table 34 are, — 



1st, That the greatest efFect of disturbance in increasing the horizontal component occurs 



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



About S^ 20"! P.M. and 6^ a.m. 4'> 40n» p.m. 6^ 0^ p.m. 5^ 15™ p.m. S^ 40"^ p.m. 



In the months December to February there are two maxima of the positive effect of disturbance, the second 

 maximum occurring about 6^ a.m. ; this is also shewn, though less distinctly, in the quantities for March and 

 April. The greatest positive effect of disturbance occurs latest in July and August, and earliest in the months 

 from September to February ; occurring throughout the year betwixt 3*^ p.m. and 5^ p.m. 



2d, That the greatest effect of disturbance in diminishing the horizontal component occurs 



In 



Dec. Jan. Feb. 



March, April. 



May, June. 



July, Aug. 



Sept. Oct. Nov 



About 



I'' A.M. 



, 2^ A.M. 



2^ 30"" A.M. 



5^ 40" A.M. 



llhp.M. 



A secondary negative maximum occurs in December to February, about 9*" 30™ a.m., and in March and April 

 about 8*" 30™ a.m. The greatest negative effect of disturbance on the hourly mean position, occurs earliest in 

 the months September to November, namely about ll^^ p.m., it occurs farther and farther after that hour in 

 the months following, till July and August, when it occurs about 5^ 40™ a.m. 



3c?, From what has been said, No. 72, the hours when the effect of disturbance is zero must be less certain, 

 they are from Table 34. 



In Dec. Jan. Feb. 



About 4:^ AM. IC" A.M. 8'" p.m. 



March, April. 

 IQl' A.M. 8^ P.M. 



May, June. 

 Ill'" A.M. 8^'' P.M. 



July, Aug. 

 0^^ P.M. 81'> P.M. 



Sept. Oct. Nov. 

 ll*" A.M. 7" P.M, 



