346 
BIGELOW. 
may befall any investigator, no matter how honest and in¬ 
telligent, when groping in the dark after the hidden facts of 
nature, and it is no discredit to him that the advancement 
of science discloses this state of affairs. Indeed, so far the 
history of the progress of science has consisted chiefly in the 
superseding the views of one generation by those of another, 
which possesses wider knowledge and deeper experience 
derived from trial and practice. (1) For nearty a hundred 
years the problem has been before magneticians regarding 
the cause of the great disturbances which occasionally sweep 
over the earth’s magnetic field and stir up currents of elec¬ 
tricity in the crust of the earth, sometimes so strong as to 
paralyze the operations of the electric telegraph lines. It 
was always assumed that the disturbances and the ordinary 
diurnal variations of the needle had the same source. Care¬ 
ful investigation of the subject was made mathematically 
by reference to certain observations, and it was concluded 
that the sun as a magnet could not be depended upon to 
produce such effects without imposing excessive conditions. 
The development of two independent external magnetic fields 
surrounding the earth, having their seat respectively in two 
distinct physical conditions, as given by a discussion of the 
observations, has recently placed the problem in a new light ; 
for it is shown that the disturbances belong to one of these 
fields, and the diurnal variations to the other, and that thus 
the early efforts to elucidate the subject were based on identi¬ 
fying two things which are really independent. Such is the 
criticism that has been recently advanced in this direction, 
namely, that the old position of magneticians fails because 
these two phenomena have different sources, while it was 
assumed that the same physical condition was behind each 
of them. (2) I have also ventured to make a criticism of 
about the same kind, though in connection with a much 
more difficult subject and one which may properly be held 
open for further discussion. It has been assigned by a very 
eminent authority as a reason for excluding the sun from 
consideration as an important agent in the disturbance of 
