rt 
ON COMPARISON AND REDUCTION OF MAGNETIC OBSERVATIONS. 235: 
7 
Wild’s Normal Days—all Days (Annual Means). 
Year | Declination Horizontal Force Vertical Force 
1893 +0'3 +1075 x 40 —10-* x 20 
1894 +0"6 +1078 x 60 —107*x 10 
There would thus appear to be no essential change in the phenomena 
since the period to which Miiller’s paper refers. 
§ 6. Wild’s ‘quiet’ days numbered only twenty-five in 1893 and 
thirty-three! in 1894, as against the Astronomer Royal’s sixty a year ;. 
thus the results from the latter are likely to exhibit even less irregularity 
in their departures from the results of unrestricted days than the former. 
Mere surmises such as the preceding are vastly inferior to the actual 
numerical facts. Before deciding on the labour necessary to obtain the: 
facts one has first, however, to estimate their probable value. One factor 
in this consideration which the practical man can fairly urge is that 
accuracy in absolute value to anything like 1 x 10~°, in the case even of 
the horizontal force, is an ideal we can hardly claim to have reached in 
this country. 
Relation of Non-cyclic Effects to Diurnal Ranges. 
§ 7. An idea of the amount of uncertainty which the non-cyclic effect. 
may introduce into the mean diurnal inequalities for summer, winter, and 
the whole year may be derived from Table V. It gives the ranges of the: 
elements, uncorrected for non-cyclic effect, as published annually in the: 
Kew ‘ Report,’ along with particulars as to the ratios borne by the mean. 
non-cyclic effects to the corresponding ranges. 
TaBLE V.—Ranges of Elements from Annual Kew Reports. 
| = 
Declination re we Force) goon Inclination 
7” Win- Sum- 7 Win- | Sum-| ~ Win- | Sum-| ,, Win- | Sum- 
Yeat ter mer Year ter mer | Year ter mer Year ter | mer |. 
/ / / i / i 
1890 6°9 51 87 21 14 30 _— _ — — — _ 
1891 8-2 6°0 102 29 20 40 14 9 20 17 11 2:3 
1892 9°6 6°9 12:3 33 26 44 17 Il 25 2°0 15 27 
1893 101 74 13:0 37 29 46 18 10 25 2:2 7) 2:8 
1894 93 70 11°9 36 26 48 17 11 22 2:2 15 28 
1895 85 56 121 33 20 46 15 10 23 2-0 12 2:8 
Means . a 8°8 6:3 114 32 23 42 16 10 23 2-0 14) 27 
(Non-cyclic B 
Effect) + 
(Uncorrected ; 
range) -| +°008 | +°033 | —-006 | +°12 | +°19 | +:07 | —-05 | —-08 | —-04 | —"13 | —:21 | —-08 
—— 
In the case of the vertical force and inclination the year 1890 has been 
omitted, as the results for it are not altogether complete. 
? The number in most of the earlier years dealt with by Dr. Miiller seems, how-. 
ever, to have been considerably greater. 
