47 
of Edinburgh, Session 1878 - 79 . 
that a telephone circuit was completed through the spring which, 
carries the pricker, the pricker itself, and the cylinder. When 
the pricker was allowed to press hard into the groove, and the 
cylinder turned, a faint grating noise was heard in the telephone, 
unless at those points where there happened to have been regular 
serrate markings left by the tool in cutting the groove, and then, as 
the pricker passed over these, a sound more or less resembling a 
feeble attempt at an articulation was heard. I then put a sheet of 
tinfoil on the phonograph cylinder, and spoke a sentence loud and 
distinct into the mouthpiece, and, for the purpose of increasing the 
sound, as heard in the telephone, I also included two Bunsen’s cells 
in the circuit. When the phonograph was now turned, so as to re- 
produce the sentence, the articulation was heard in the receiving 
telephone, loud enough certainly, but considerably marred by the 
mere rasping of the pricker on the natural inequalities of the 
tinfoil. 
It is obvious that, in this experiment, the articulation, such as it 
is, heard in the telephone must be caused by the variation in the 
resistance to the current, which arises from the unequal pressure of 
the pricker upon the tinfoil as it follows its indentations. This has, 
I think, an important bearing upon the character of all curves got 
by different processes of enlargement from the tinfoil record. Such 
curves could only accurately correspond to the movements of the 
disc which produced the indentations, provided the style attached 
to the lever, for producing the enlargement, pressed exactly on the 
tinfoil as the pricker did. Now, seeing that the pricker does not 
press equally at all times on the tinfoil, it would be very difficult, 
if not impossible, so to arrange a style and enlarging lever as to press 
in a manner so exactly similar. 
The telephone can be employed to illustrate, in a very pleasing 
way, the incipient stage in the breaking-up of a liquid vein into 
globules. For this purpose a vein of acidulated water is made part 
of a telephone circuit, which also includes one or two Bunsen cells. 
This is easily managed by attaching a metallic can, having a small 
orifice in its bottom, to one of the terminals of the circuit, and a 
shallow metallic basin to the other. The first vessel, being now filled 
with acidulated water, is held over the basin, so that the column of 
water from the orifice flows into it, and so completes the electric 
