234 REPORT—1896. 
Mean Annual Values from ‘ Quiet’ and Unrestricted Days. 
§ 4. Table IV. is merely a plain statement of facts ; but if too exclu- 
sively considered it might unquestionably convey an exaggerated idea of 
the defects attaching to the ordinary use made of ‘quiet’ days at the pre- 
sent time. At Kew Observatory they are employed to get out the mean 
diurnal inequality for summer and winter and the whole year, as well as 
the mean annual values of the several elements. 
As regards the mean annual value of an element, the quantity 
‘mean value from “ quiet” days less mean value from all days’ may be 
irregularly positive and negative, or like the non-cyclic effect in the 
element it may be normally of one sign. It would certainly be desirable 
to know which of the alternatives is true. The meaning to be attached 
to the secular variation deduced from two consecutive years or from a 
short series of years would be much more uncertain if the former 
alternative represented the facts than if the latter did. 
In the Greenwich ‘ Magnetical and Meteorological Observations’ tables 
are published showing the diurnal variations both in ‘ quiet’ and unre- 
stricted days, but not apparently direct information as to the difference 
between the absolute values of means deduced from the ‘ quiet’ and from 
unrestricted days. ; 
At St. Petersburg, and then at Pawlowsk, it has, however, long been 
customary for Dr. Wild to select a series of normal ‘quiet’ days whose 
results are dealt with alongside of those from unrestricted days. The 
principle of selection guiding the choice at Pawlowsk and Greenwich has 
probably been slightly different, but there is at least a strong presumption 
that the differences between the annual means from unrestricted days and 
from the Astronomer Royal’s ‘ quiet’ days will prove to be of the same 
character as the corresponding differences observed in the case of Wild’s. 
‘quiet’ days. 
§ 5. The annual means for all the elements at St. Petersburg, from 
both ‘quiet’ and unrestricted days, for some twelve to sixteen years 
preceding 1885 are given in a paper by Dr. Miiller in the ‘ Repertorium 
fir Meteorologie,’ Bd. XII. No. 8. In the case of every element, according 
to Miiller’s tables 20 to 23, the sign of the quantity ‘ “ quiet ” day mean 
less unrestricted day mean’ was uniformly, or practically uniformly, of 
one sign ; and the secular variations deduced from the ‘quiet’ and un- 
restricted day results, even for consecutive years, showed a remarkably 
good agreement. The following summary of the mean results deducible 
from Miiller’s tables is extracted from a recent paper by Leyst ! :— 
Wild's Normal Days—all Days (Annual Means). 
Declination west . PhO e2o: 
Inclination . { . — 0723. 
Vertical component - —10°x8C.G.S. units. 
Horizontal component . +107§x 35 Af 
Tables of the monthly and yearly means for Wild’s ‘quiet’ days and 
for unrestricted days at Pawlowsk continue to be given in the ‘ Ann. des. 
Phys. Central-Observatoriums.’ The results from the last two volumes 
are as follows :— 
1 Rep, fiir Met, BA. XVII. St. Petersburg, 1894, No. 1, p. 109. 
