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general use in practice, give the strongest sound and although 
theoretically they ought to articulate less accurately than coils with 
more primary wire and no iron, in practice this is not at all perceptible, 
not even in laboratory-practice, which is the only practice I havea 
right to speak of. Our sense of hearing is evidently so accustomed 
to content itself with defective sounds and to understand them that 
we cannot at all observe the small differences in the accuracy of 
the reproduction, which must undoubtedly exist when using the 
different coils. 
I cannot omit quoting some lines of HeaAvisipr, ') who expresses 
himself as follows, after having enumerated the different distortions 
to which telephonic transmission is exposed before the sound of the 
telephone is observed by us: 
“And yet, after all these transformations and distortions, practical 
telephony is possible. The real explanation is, I think, to be found 
in the human mind, which has been continuously trained during a 
lifetime (assisted by inherited capacity) to interpret the indistinct 
indications impressed upon the human ear; of which some remarkable 
examples may be found among partially deaf persons, who seem to 
hear very well when all they have to go by (which practice makes 
sufficient) is as like articulate speech as a man’s shadow is like 
the man.” 
As respects practice it is evident that nothing is to be learnt from 
my paper. The only thing deducible from it, is perhaps the following: 
On very long telephonic cables where all slight influences which 
might weaken the transmission of the sound, must be avoided, it is 
the custom that each station shunts the secondary of its induction- 
coil during the time that it takes a message, by pressing down a 
button. The telephonic currents coming from the sending station need 
not in this way pass through the secondary of the receiving station 
and are not needlessly weakened by the self-induction of that secondary 
with iron core. If now we were to take a coil with more primary 
layers and no iron, the self induction of the secondary would be much 
smaller and the troublesome shunting during the listening might 
perhaps be avoided. But no doubt the shunting of the coil is the 
more efficacious means to prevent the weakening of the telephonic 
currents. 
1) Oxrver Heavasipe, Electrical Papers, Vol IL, Page 348, 
