488 Dr. £. Naumann—Magnetism and Earth Structure. 
tion of errors is to be attempted. Though errors of observation cannot 
be avoided, there is no doubt that in many cases deviations from a 
certain expected result are not due to errors, but to actual irregu- 
larities presented by nature. These deviations were formerly 
referred to accidental causes or to local influences, and the unexpected 
results were considered anomalous and disappointing; and even up 
to the present day it has been customary to arbitrarily modify results 
which do not agree with mathematical formulas, and to constrain 
curves that would not otherwise have exhibited the expected 
regularity. 
The earth’s crust is considerably broken and fissured, and its 
superficial layers folded; these disturbances must have some influence 
on the phenomena resulting from the motions which we call heat, 
electricity, and magnetism. Of these forces, magnetism is the one 
most useful in the study of the earth’s structure, and just as optical 
phenomena are employed in researches on the internal structure of 
crystals, those of magnetism may be used to investigate the internal 
structure of the globe. Magnetic phenomena may be regarded as 
telegraphic messages from distant depths, but, unfortunately, in the 
present state of science, it is impossible to decipher them. 
In a memoir entitled “The Phenomena of Terrestrial Magnetism 
in their Dependence upon the Structure of the Earth’s Crust,’? I 
have given a large number of instances in which the distortion of 
magnetic curves are caused by clefts in the crust, and have pointed 
out that the isogonic lines afford the clearest indications of a con- 
nection between magnetic and structural conditions. The ‘isogones ’ 
are much more important than the magnetic meridians; this will be 
easily understood as soon as electricity and magnetism are considered 
to be different manifestations of one and the same force. From 
recent investigations made in Germany it is highly probable that an 
intimate connection exists between Earth Currents and Terrestrial 
Magnetism, and if this be true, deviations in the direction of the 
currents ought to be accompanied by changes of declination. For 
such reasons I consider the Isogones to be the best indicators of the 
course of the earth-current. 
The systems of magnetic curves show very distinctly a relation 
to mountain ranges, faults, eruptions, and tectonic disturbances, 
wherever a detailed magnetic survey has been made. Irregularities 
in the curves are so frequent that their existence could not be denied 
even at the very beginning of magnetic surveying; however, they 
were not attributed to want of internal uniformity of the globe, but 
to the influence of magnetic masses at or near the surface, to denote 
which, the special name ‘“‘ Rock Magnetism” was introduced. There 
are magnetic rocks at the surface. and almost any kind of rock, such 
as Serpentines, Granites, Syenites, Porphyries, Diorites, Trachytes, 
Andesites, Basalts, etc., may act on the needle, but there are no 
magnetic rocks below the surface! Even magnetic iron ore does not 
show a trace of magnetism directly after it is taken from the mine, 
1 Die Erscheinungen des Erdmagnetismus in ihrer Abhiangigheit von Bau dei 
Erdimde, Stuttgart, 1887 
