248 M. Werner Siemens on the 
magnetic susceptibility of 480 to 500, when that of air is taken 
equal to 1. The experiment was repeated with greater dis- 
tances apart of the plates, and further with iron wire, sheet- 
iron, and prismatic rods of iron, and the same ratio was 
obtained. 
The question next presented itself whether this resistance of 
the air, amounting to some 500 times the resistance of iron, was 
not in part to be ascribed to the magnetic oxygen contained 
inthe air. In order to investigate this, | connected two round 
iron plates of 8 millim. diameter by means of a ring of brass — 
soldered to them. By means of tubes closed by taps fitting 
into two openings in the brass ring, it was possible to fill the 
space between the metal plates, which were 5 millim. apart, 
with any desired gas or to exhaust the chamber. The iron 
plates thus connected were fastened to the pole-pieces of the 
electromagnet, and the magnetic moment of the magnetic 
circuit measured for different current-strengths. Not the 
smallest difference could be observed whether the space between 
the plates was filled with air, oxygen, or hydrogen, or whether 
it was exhausted as completely as possible by means of the 
mercury-pump. 
It follows therefore that the magnetic properties of oxygen, 
and in general the influence of matter, with the exception of 
iron and the other so-called magnetic metals, upon the magne- 
tization only become of influence with very great magnetic 
moments, such as those with which diamagnetic phenomena 
occur, and that for nonmagnetic substances, only the geo- 
metrical conditions of space need to be taken into account in 
magnetic phenomena. Whether this will not lead us, in ac- 
cordance with the views of Secchi and Hdlund, to replace the 
Amperian molecular circuits by ether-vortices which fill all 
space, but are present in magnetic substances only in greater 
number or of greater intensity, may remain here undiscussed. 
The striking fact that a vacuum permits magnetic distribution 
and attraction like nonmagnetic matter would, however, be 
explained by it. 
That space filled with nonmagnetic material as well as a 
vacuum is affected by electric currents quantitatively exactly 
in the same way as iron in its condition of greatest magnetic 
susceptibility, but some 500 times less energetically, is seen 
from the following experiment. I had two coils made of 
insulated wire 1 millim. thick, of 87 millim. diameter, and 100 
millim. length, and placed them with axes parallel and at a 
distance apart of 131 millim. The pole-surfaces of these 
solenoids opposite each other were each covered by an iron 
plate, which was wound between the solenoids, with an 
