No. I PERIODS RELATED TO 273 MONTHS—ABBOT 5 
These periodicities in weather cannot be satisfactorily demonstrated 
without attending to several steps made necessary by changes of the 
atmosphere. 
1. Normals and departures must be separately tabulated for times 
of high Wolf sunspot numbers, and of low Wolf numbers. I am 
accustomed to drawing the line at 20 Wolf numbers. 
2. For all the shorter periods (1.e.,.<15 months) the months of the 
year must be used in several separate groups because atmospheric 
conditions differ. I am accustomed to dividing the year into three 
groups: January-April, May-August, September-December. I omit 
this grouping after periods of 15 months. Beyond that, too few col- 
umns would generally be available in a tabulation, and the division of 
the year into several groups is less important compared to the length 
of periods. The division of data into three groups mentioned above 
indeed leaves the tables with too few columns to yield satisfactory 
means. Therefore I make the assumption that the form and amplitude 
of periods in different seasons will be sufficiently similar to permit 
combination of six separate tables for the three seasons and two 
ranges of Wolf numbers into one by shifting them all to a common 
phase. But when such a combined table is used in a synthesis its gen- 
eral mean must always be restored to the proper phase in the synthesis. 
3. As the earth is copiously bombarded with solar ions when sun- 
spots are numerous, and these ions act to produce haze in the at- 
mosphere, it is also necessary to separate tabulations for high and low 
Wolf numbers. I am accustomed to drawing the line at 20 Wolf 
numbers. 
4. As the growth and shifting of populations and the invention of 
new devices, such as automobiles and airplanes, operate to alter the 
atmosphere, it is necessary to make a division of data for this. I am 
accustomed to drawing the line at the year 1900. That is not really 
adequate, but perfection is beyond reach, for with 23 periods to be 
synthesized, the precautionary measures mentioned above require 186 
tables to be used. 
5. As there are many periods, all exact aliquot parts of 273 months, 
it follows that most tabulations for a selected period are encumbered 
by shorter periods, exact aliquot parts of the period tabulated. I am 
accustomed to plotting the mean result of such a tabulation, scanning 
the graph for superriders, and, one after another, computing form and 
amplitude of these superriding periods, and removing them by sub- 
traction till the wanted period stands out alone. 
