1905-6.] Electric Oscillations and Magnetic Properties of Iron. 45 
Hence in my opinion Marconi’s second instrument detects * the 
increase of induction which occurs when electric space waves are 
superposed upon field at or near a cyclic extreme, in precisely the 
same way as Rutherford’s original apparatus detected, or rather 
measured, a decrease at another point of the cyclic process. 
The function of the moving band appears to be twofold : — 
first, it supplies the hard iron or steel in a condition of lower 
permeability, in order that it may be raised to a condition of 
higher permeability when the signals are received from a distant 
station ; and second, it distorts the field in the direction of motion, 
the telephone thus tending to respond in a greater degree to 
signals received when the field is increasing near but not at the 
cyclic extreme. It has already been pointed out that for low field 
this is the most sensitive part of the cycle. 
Third. The Ewing-Walter form of detector is essentially 
different from those already discussed. It is based upon Ewing’s 
hysteresis tester, which measures the drag between field and iron 
when one of these is revolving. The best speed is stated to be 
from five to eight revolutions per second, while Marconi obtained 
good results at a speed of only half a revolution per second. The 
reason for this great difference is obvious. The Marconi instruments 
detect instantaneous induction change (A conditions), while the 
Ewing-Walter form integrates (B conditions). 
The inventors anticipated that the receipt of electric waves 
would be detected by a fall in the normal deflection, in accordance 
with what appears to have been the generally accepted but 
erroneous view that oscillations in all cases cause a diminution of 
the energy loss per cycle. A fall in the normal deflection was 
at first obtained when the oscillations may be supposed to have 
been co-directional oscillations, and thus to alternately assist and 
oppose the field. On experiments being continued, however, an 
increase in the normal deflection resulted, but in this case the 
oscillations were passed directly through the iron or steel core, 
thus giving rise to transverse oscillations. 
The former result — a decrease of energy loss, due to oscillations — 
is not in harmony with my experimental results for low fields. 
A probable explanation may be found in the fact that in my case 
* Or even measures, provided the signalling is not proceeding too rapidly. 
