The values for 1843 are interpolated as in the preceding two months Constant correction + 14 845 839 827 824 822 822 827 827 830 830 828 827 Monthly mean normal from the even hours (+ 214m) 828.2, weight 5. Referred mean 1077 1072 1067 1065 1065 1067 1071 1073 1075 1077 1077 1078 858 846 845 854 857 857 860 855 848 847 847 851 856 858 859 858 859 859 Monthly mean normal from the even hours (+ 211m) 856.6, weight 5. 66 66 66 odd 66 66 TABLE I.-RECAPITULATION OF THE HOURLY NORMALS OF THE HORIZONTAL FORCE (EXPRESSED 803 802 801 800 799 797 795 799 804 812 817 822 824 823 823 820 818 817 817 820 829 841 849 851 834 833 830 771.5 769.8 769.1 767.4 765.7 763.7| 761.9 766.7 773.7 781.3 786.1 786.5 801 800 801 802 800 800 803 805 804 828 827 782.9 776.2 769.5 766.5 766.2 768.6| 771.6 772.6 773.4 773.5 773.4 772.8 787.7 782.3 777.0 772.8 772.0 773.3 774.2 774.8 775.2 774.8 775.2 774.8 In the preceding table the normals for the summer half year comprise the months between April and September inclusive; those for the winter half year comprise the months between October and March inclusive. The following table contains the mean values of the normals for each month and Regular Solar-Diurnal Variation of the Horizontal Force.-If we subtract the hourly normals of Table I. from their respective monthly mean value as given in Table II., the difference (in scale divisions) will represent the regular solar-diurnal : variation for each month in the year. In like manner we obtain the diurnal variation of the horizontal force-free of the larger disturbances-for the summer and winter half, and for the whole year. year. Table III. will exhibit these differences after their conversion from scale divisions into parts of the horizontal force (one scale division equalling 0.0000365 parts of the horizontal force). The tabular numbers are expressed in units of the sixth place of decimals. sixth place of decimals. A plus sign indicates a greater force, a minus sign a less force than the mean value. Casting the eye over the vertical columns, we obtain also a view of the annual inequality of the diurnal variation, which will be examined further on. 0.000 0.000 TABLE III.-REGULAR SOLAR-DIURNAL VARIATION OF THE HORIZONTAL COMPONENT OF THE MAGNETIC FORCE EXPRESSED IN PARTS OF THE HORIZONTAL FORCE. A plus sign indicates greater force than the mean. For convenience sake, the first three decimals (0.000) have been placed on the side of the table. 1840-1845. Oh 1h 2h July April June Year Summer 4h 5h 6h 7h gh 9h 10h 11h+211m -499 3h 098 +134 +171 +207 +244 +317 +390 +244 +061-230-412-595 1840-1845. 12h 13h 14h 15h 16h 17h 18h 19h 20h 21h July November December January April June Year Summer Noon. 22h 23h+211m -244 +157 +485 +595 +631 +376 +047-025098-171-244-244 0.00 TABLE IV. Table IV. is derived from Table III. by multiplication with the absolute value of the horizontal force (4.173); it contains, therefore, the regular solar-diurnal variation of the horizontal force in absolute measure. A plus sign indicates greater force than the mean. Two places of decimals have been placed on the side of the table. 1840-1845. Oh 1h 2h 3h 4h July September October June Year 6h 7h 8h 9h 5h -165 1840-1845. 12h 13h 14h 15h 16h 17h 18h 19h 20h 21h 22h 23h+211m July October April May June Year Noon. -102 +065 +203+248 +263 +157 +020-010-041-071-102-102 -021-011 Annual Inequality in the Diurnal Variation of the Horizontal Force.-The distinctive feature of the diurnal variation is shown in the annexed diagram (A), constructed from the mean annual and half-yearly values given in the preceding table, IV. It exhibits in the annual mean, as its characteristic type, a maximum value about 6 A. M., a minimum value about 11 A. M., a secondary maximum value about 3 P. M., and a secondary minimum about 9 P. M. For the half year when the sun has north declination, the morning minimum becomes smaller and the afternoon maximum larger, thus increasing the diurnal range; the converse takes place in the other half of the year, when the sun has south declination. The 6 A. M. maximum remains nearly unchanged throughout the year. The average summer range (April to September inclusive) is 0.0046, and the average winter range (October to March inclusive) is 0.0025, both expressed in absolute measure. The range between the morning maximum and the morning minimum is 0.0045 in summer and 0.0036 in winter, as will be explained further on. |