417 
ON “QUIET” DAYS DURING THE ELEVEN YEARS 1890 TO 1900, ETC. 
§ 51. Ihe variation of “ a throughout the year in Table XL. is fairly similar to 
what we have already observed in the case of the ranges from 11 year means. There 
IS a conspicuous minimum in winter, usually in December, and at least a trace of a 
second minimum near midsummer. The fluctuations of h and of h/a from month to 
month are somewhat irregular, and are doubtless in part purely accidental. It would 
probably require a long series of years, including several sun-spot cycles, to give a 
smooth annual variation. The general features are however clear enough, and may 
be easily grasped from a comparison of tlie mean values assigned to the three seasons. 
In all four elements h is decidedly least, but h/ft decidedlv greatest, in winter. A 
smaller value of h implies a smaller absolute increase to the value of an element for a 
gi\en increase of sun-spot frequency. A larger value of h/a means a larger percentage 
change in the element for a given change in sun-spot frequency. 
Ihe \alue of appears less m summer than at the equinox m all four elements, 
and this is even true, though inucli less conspicuously, of the value of h itself in all 
the elements except V. 
For such practical purposes as navigation and survey work the value of h is 
piobably the most important thing, but for theoretical work, especially when dealing 
with data from a single station, the value of b/a will probably prove to possess more 
significance. If we divide tlie yearly and seasonal values of {b/a) X 10 ^ in Table XL., 
by 5, 4, 3 and 2 respectively, we get the following results, going to the nearest 
integer ;— 
Year. 
Winter. 
Equinox. 
Summer. 
IdV'O io‘ ill I .... 
22 
.33 
23 
17 
-1 {!>/(() 10^ in 11. 
OD 
.3G 
23 
IG 
i (h/a) 10^ in D. 
I'l 
.33 
0 0 
IG 
4 {h/a} lOMn V . 
00 
35 
21 
19 
Mean. 
22 
34 
0 0 
17 
le 
I his brings out the remarkable similarity in the seasoiial changes of hj(t iu the 
diffeient elements, and the closeness between the values of h/'ft for the equinox and 
for the year as a whole. 
^ Wlulst the sun-spot influence as given by Table XL. is decidedly least for V, fh. 
difference from the other elements is less than would appear from the “ Preliminaiv 
Note. The results given there for V were appreciably influenced by the neglect of 
the temperature correction in years prior to 1897, already explained in § 19. The 
omission of the correction diminished the range in V, and brought its values in years 
piior to 1897 mostly years of large sun-spot frequency—closer to the values in the 
later years than they ought to have been. 
VOL. LOT I .—A, 
3 H 
