244 
I)R. C. CHBEEj MAGNETIC DECLINATION 
Mean of absolute ranges on the ten 
days of— 
Mean of absolute ranges on the five 
days of— 
Largest range. 
Least range. 
Largest range. 
Least range. 
/ 
7-3 
3-0 
/ 
9-4 
/ 
2-7 
The two days having the absolutely largest ranges were the 27th and 28th, and so 
were preceded by over 30 days free from spots. 
The above instances are probably amongst the most striking examples of their kind, 
but many others scarcely less striking could be adduced. No doubt a similar number 
of striking associations of large ranges and large sunspot areas exists, but if the one 
set of phenomena must be ascribed to chance, may not also the other ? 
The phenomena of December, 1900, alone suffice to demonstrate that considerable 
variations are possible in the range without the occurrence for a month previously of 
any sunspot of measurable area. Thus, unless a time lag exceeding a month is 
postulated, we seem obliged to conclude that there are agencies other than those 
associated with visible sunspots which exert a potent influence on the range of the 
magnetic needle. The immediate source may, of course, be the sun, if the visible 
sunspot is only an accidental concomitant of the electrical disturbance and not an 
essential phenomenon. But it seems equally possible that the disturbances at the 
sun, visible as sunspots, and the enlargement of the magnetic range, are due to a 
common cause, operating throughout the solar system, but with an intensity which at 
any given instant may vary widely at points as far apart as the earth and sun. 
One possibility which may be mentioned, if only to show that it was not overlooked, 
is that the ions, electrons, emanations—or whatever is the appropriate term for the 
entity supposed to be propagated from the sun—may have properties which show 
only a gradual decay when in the earth’s atmosphere. Thus the condition on any 
given day, in that part of space—if external to the earth’s surface—whence originate 
the causes of magnetic movements, regular and irregular, may be represented by an 
integral which receives contributions from a number of previous days. This is at 
least consistent with the continuous large amplitude of the diurnal inequality which 
is characteristic of years of many sunspots. 
It must be remembered, however, that disturbances seldom continue large for more 
than two or three days, often less, and that quiet days often follow hard on them ; 
on the other hand, magnetic storms often reach a great intensity within a few hours 
after a prolonged quiet or but slightly disturbed time. The immediate cause of at 
least some forms of magnetic disturbance must thus be something which is capable of 
very rapid changes, and whose effects may die out, if not instantaneously, at least 
very rapidly. 
