ox “QUIET” DATS DURING THE ELEVEN YEARS 1890 TO 1900, ETC. 
337 
Table I. — Sun-Spot Frequency (after Wolfer). 
1890. 
1891. 
1892. 
1893. 
1894. 
1895. 
189G. 
1897. 
1898. 
1899. 
1900. 
Means 
for each 
montli of 
the year. 
January . 
5-3 
13-5 
09-1 
75-0 
83-2 
G3-3 
29-0 
40-G 
30-2 
19-5 
9-4 
39-8 
Februaiy . 
0-G 
22 • 2 
75-G 
73-0 
84-G 
G7-2 
57-4 
29-4 
3G-4 
9-2 
13-G 
42 - G5 
March . 
5-1 
10-4 
49-9 
G5 • 7 
52 - 3 
Gl-0 
52-0 
29-1 
38-3 
18-1 
8-G 
35-5 
April . . 
1-G 
20-5 
G9-G 
88-1 
81 -G 
7G-9 
43-8 
31-0 
14-5 
14-2 
lG-0 
41-G 
May 
4-8 
41-1 
79-G 
84-7 
101-2 
G7-5 
27-7 
20-0 
25-8 
7 -7 
15-2 
43-2 
June . . 
1-3 
48-3 
76-3 
88-2 
98-9 
71-5 
49-0 
11-3 
22 ■ ?> 
20-5 
12-1 
45-4 
July . . 
11-G 
58-8 
7G-8 
88-8 
lOG-0 
47 - 8 
45-0 
2 7 - G 
9-0 
13-5 
8-3 
44-8 
August 
8-5 
33-2 
101-4 
129-2 
70-3 
G8-9 
27-2 
21-8 
31-4 
2-9 
4-3 
45 - 4 
September 
17-2 
53-8 
G2-8 
77-9 
G5-9 
57 - 7 
Gl-3 
48-1 
34-8 
8-4 
8-3 
45-1 
October . 
11-2 
51-5 
70-5 
79-7 
75-5 
G7-9 
28-4 
14-3 
34-4 
13-0 
12-9 
41-75 
November 
9-G 
41-9 
G5-4 
75-1 
5G-G 
47-2 
38-0 
8 * 4 
30-9 
7-8 
4-5 
35 - 0 
Decern l)er. 
7-8 
32-2 
78 • G 
93-8 
GO-0 
70-7 
42-G 
33-3 
12-G 
10-5 
0-3 
40-2 
Means for 
individual 
years . . 
7-1 
35 • G 
73-0 
84-9 
78-0 
G4-0 
41-8 
2G-2 
2G-7 
12 1 
9-5 
41-72 
Secnhir (Jhangr. 
§ 3. Few people at all a})preciate the diffieulty of arrivino' at anytliing apjjroaclhng 
certainty as to the true value of the secular chano’e of mao’uetic elements from one 
year to the next. An examination of the puhlislied records of any two observatories, 
at such moderate distances apart as Potsdam and Parc St. Maur (Paris), or even 
when so close too^ether as Kew and Greenwich, discloses irreoadarlties which are not 
shared by the two stations. In the present state of our knowledge, we can only say 
tliat such Irreg’ularities may he ahsolutely faitliful representations of the operations of 
Nature, but per.sonally I am Inclined to the belief that they often owe a good deal to 
instrumental or similar causes. Building operations, changes of instruments, of 
oh.servers, or of methods of reduction, are all apt to influence ohsei'vational results, 
and of late years electric trams have been wreckino; observatories, or introducing 
uncertainties into tlieir records, all over the world. In the present case, this last and 
worst cause of uncertainty mav Ije left out of account, hut some of the others liad, 
unfortunately, to be dealt with. Wlienever it appeared necessary, I have referred t(j 
the original records, and have calculated so far as possible what the results would 
have been if the methods and instruments employed had been the same as of late 
years. To explain the situation, a brief account is necessary of the present method of 
deducing results from the measurement of tlie curves. To economise space, I shall 
throughout the rest of the paper distinguish the several magnetic elements by letters, 
and employ the,se, when convenient, in the text and tables. The letters so employed 
and their meanings are as follows :— 
O 
VOL. CCir,-A. 2 X 
