FUNCTION OF CRITICISM IN ADVANCEMENT OF SCIENCE. 345 
nomen on in question, and the application is made to the 
wrong case: (1) Several years ago an attempt was made to 
explain the peculiar curvature of the rifts of the solar corona 
which are photographed during an eclipse by comparing them 
with the lines of force surrounding a spherical magnet with 
uniforhi internal magnetism. A critic drew out his equa¬ 
tions and the corresponding lines of force and claimed that 
they did not agree as was supposed. A brief examination of 
the formula revealed the fact that he had taken the com¬ 
panion case of a spherical magnet immersed in an independ¬ 
ent external field, which changes the form of the curves near 
the surface. He simply applied the wrong case. (2) Another 
somewhat similar instance, but more complex in its details, 
came also to my notice. Three cases may occur in which 
the lines of force in a uniform magnetic field are distorted 
by placing a permeable substance within it, since the lines 
always seek the path of least resistance. The first is where 
a spherical solid as an iron sphere is placed in such a field, 
the lines taking on a system of curves determined by the 
strength of the field, the permeability and shape of the solid; 
secondly, if a spherical shell with a hollow interior is placed 
in the same field the lines assume similar but really different 
curves, and a part of them pass across the hollow (Barlow’s 
Problem); if in the third case there is a permeable shell 
filled up with a substance impenetrable to magnetic lines, 
then the curves are different from either of the other cases, 
being more sharply exflected at the poles. It has been my 
conclusion that the earth, having a permeable shell and being 
filled with a material nucleus which entirely turns aside the 
lines of an external magnetic field, is comparable to the third 
case, and that in this way a number of observed phenomena 
find their explanation. A critic, however, carefully worked 
out the consequences of the second case and found that it 
did not agree with my exhibition of the phenomenon. It was 
contended that this criticism is inapplicable, because of mis¬ 
taking the case which ought to be employed. 
Mistaken identity is an exceedingly common error which 
50-Bull. Phil. Soc., Wash., Vol. 13. 
