xl 



Geneeal Results of the Makeestoun Obseevatioxs. 



Table 33. — Diurnal Variations of the Horizontal Component of Magnetic Force for DiflFerent 

 Periods, deduced from Days selected as free from Irregular Disturbances, in the Years 1844 

 and 1845. 















Six Months. 





Mak. 

 Mean 

 Time. 



Dec. 

 Jan. 

 Feb. 



March. 

 April. 



May. 

 June. 



July. 

 Aug. 



Sept. 

 Oct. 

 Nov. 







Twelve 

 Months. 



Sept. to 



March 















Feb. 



to Aug. 





h. m. 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



12 12 



-0098 



+ 0283 



+ 0244 



+ 0287 



+ 0190 



+ 0046 



+ 0271 



+ 0159 



13 12 



-0168 



+ 0181 



+ 0106 



+ 0160 



+ 0131 



-0018 



+ 0149 



+ 0065 



14 12 



-0158 



+ 0073 



-0002 



+ 0044 



+ 0138 



-0010 



+ 0038 



+ 0014 



15 12 



-0066 



+ 0007 



-0104 



+ 0002 



+ 0180 



+ 0057 



-0032 



+ 0012 



16 12 



+ 0038 



+ 0034 



-0152 



-0072 



+ 0240 



+ 0139 



-0063 



+ 0037 



17 12 



+ 0176 



+ 0153 



-0313 



-0236 



+ 0279 



+ 0227 



-0132 



+ 0047 



18 12 



+ 0206 



+ 0072 



-0555 



-0512 



+ 0151 



+ 0178 



-0332 



-0076 



19 12 



+ 0210 



-0163 



-0880 



-0945 



-0138 



+ 0036 



-0663 



-0313 



20 12 



+ 0057 



-0687 



-1363 



-1514 



-0734 



-0338 



-1188 



-0763 



21 12 



-0142 



-1230 



-1723 



-1908 



-1217 



-0679 



-1620 



-1149 



22 12 



-0380 



-1610 



-1815 



-1948 



-1434 



-0907 



-1791 



-1349 



23 12 



-0422 



-1471 



-1461 



-1506 



-1107 



-0764 



-1479 



-1122 



12 



-0251 



-1030 



-0846 



-0848 



-0706 



-0478 



-0908 



-0693 



1 12 



+ 0025 



-0464 



-0159 



-0116 



-0138 



-0056 



-0246 



-0152 



2 12 



+ 0134 



+ 0019 



+ 0232 



+ 0472 



+ 0138 



+ 01.36 



+ 0241 



+ 0188 



3 12 



+ 0115 



+ 0448 



+ 0681 



+•0887 



+ 0303 



+ 0209 



+ 0672 



+ 0440 



4 12 



+ 0145 



+ 0488 



+ 0962 



+ 0898 



+ 0438 



+ 0291 



+ 0783 



+ 0536 



5 12 



+ 0236 



+ 0671 



+ 1321 



+ 1155 



+ 0485 



+ 0360 



+ 1049 



+ 0705 



6 12 



+ 0217 



+ 0796 



+ 1410 



+ 1241 



+ 0601 



+ 0409 



+ 1149 



+ 0779 



7 12 



+ 0120 



+ 0884 



+ 1368 



+ 1276 



+ 0573 



+ 0346 



+ 1176 



+ 0761 



8 12 



+ 0060 



+ 0735 



+ 1105 



+ 1129 



+ 0510 



+ 0285 



+ 0990 



+ 0637 



9 12 



-0024 



+ 0607 



+ 0873 



+ 0877 



+ 0459 



+ 0217 



+ 0786 



+ 0501 



10 12 



-0016 



+ 0665 



+ 0628 



+ 0660 



+ 0386 



+ 0185 



+ 0651 



+ 0418 



11 12 



-0016 



+ 0545 



+ 0450 



+ 0507 



+ 0277 



+ 0130 



+ 0501 



+ 0315 



71. The following are the approximate epochs in apparent time deduced from Table 33. 

 dotted curves, Plate II.) 



Minimum, 

 Maximum, 

 Minimum, 

 Maximum, 



Dec. Jan. Feb. 



lO^^ 45™ A.M. 

 5h 30m p jyi_ 



Ih 30m A.M. 

 G^ 35™ .\.M. 



March, April. 



10"^ 25™ A.M. 



7^ 0™ P.M. 



3h 20™ A.M. 



b^ 30™ A.M. 



May, June. 

 9^ 55™ A.M. 



6'* 30™ P.M. 



July, Aug. 



9^ 50™ A.M. 

 Qh 55m p_M, 



(See also the 



Sept. Oct. Nov. 



IC* 10™ A.M. 



6^ 35™ P.M. 



Ih 55m A.M. 

 5^ 30™ A.M. 



A comparison of these epochs with those deduced from Table 32 will shew, that the effect of disturbance is 

 to accelerate the epochs of the forenoon minimum and afternoon maximum, those of the latter being most 

 affected. In the undisturbed diurnal variation the afternoon maximum occurs latest in March and April, and 

 in July and August. 



72. Diurnal Variation of the Effect of Disturbance on the Horizontal Component. — The following result is 

 obtained upon the assumption, that intermittent disturbance which affects the hourly mean position does not 

 affect the monthly mean of the 24 hours ; or, that the differences found No. 57, between the monthly means of 

 the undisturbed days, and of all the days, is due to continuous and regular laws, which have little effect on the 

 relative hourly positions ; it appears very probable from No. 58, that this assumption is not quite accurate, but 

 that the negative quantities in the following Table are too small, and the positive ones too large ; those 

 for the summer months, however, must be near the truth, as disturbance had little or no effect on the mean for 

 that group : the error in the values for the other periods cannot affect the epochs of positive and negative 



maxima. 



