625 
of Edinburgh, Session 1877 - 78 . 
used, which were the same as those employed with the tuning-fork, 
could send with a brisk turn of the hand a current induced by the 
earth, may have been so excited, but there was next to nothing 
rotational in the blow they got or gave. 
It may be well believed that many of the sounds thus produced 
in the telephone were very faint, and required a sharp ear and 
undivided attention. I have mentioned only these results which 
have been repeatedly got. Possibly some of them may be wrong as 
regards comparative loudness, but I had in almost every case the 
impression of different listeners. The listener was provided with 
two telephones of the following kind. One pole of a horse-shoe 
magnet (fig. 7), carried the bobbin pin and a brass arm for an 
adjusting screw. To the other 
an iron stage was fixed, to which 
was screwed a box 3J inches in 
diameter and J inch deep, with a 
hole in the top J inch wide, pro- 
vided with a short tube for inser- 
tion into the ear. The bottom 
of this box was of untempered 
steel plate (No. 28), and its distance from the pin could be adjusted 
by the screw. Such an instrument told faint tuning-fork sounds, 
which the ordinary one pole ferrotype plate telephone I had passed 
over. 
Leaving now the sending station, we proceed in our search 
for molecular action to the receiving instrument, and we examine 
the sounds emitted by its electric and magnetic parts. Instead 
of having a person performing the irksome task of talking or 
singing at the sending end, let us lay aside the distant telephone, 
and put in its place and that of the speaker a Bunsen cell 
charged with water and a mercury break. Such a cell would have 
no effect on the telephone without the break, for it is only momen- 
tary currents that affect the instrument. The break thus furnishes 
us with an intermittent or discontinuous current, and is in fact an 
untiring and uniform speaker, uttering a series of ticks or taps which 
are very audible to the distant telephone hearer. Now let us begin 
with the coil which is the “ fountain and source ” of all action in 
the receiver. Let us detach it from the core, and hold it up to the 
