1879J Notes . 517 
along as the writing proceeds, and the messages have only to be 
cut off from time to time, wound round a piece of card, and sent 
out to their destination, or put into an envelope and dispatched. 
Edison’s Loud-speaking Telephone was exhibited by Mr. Arnold 
White and Mr. C. P. Edison. This instrument far surpasses 
every other form of telephone at present invented. It is thus 
described by Mr. Conrad Cooke. A cylinder composed of pre- 
cipitated chalk, to which a small proportion of acetate of mercury 
is added, the whole being moistened into a saturated solution of 
caustic potash and moulded into a cylindrical form by being sub- 
jected to hydraulic pressure, is mounted upon a horizontal axis, 
and is made by suitable mechanism to revolve beneath a metallic 
strip, which is maintained with a uniform pressure against the 
surface of the chalk. At the point where the strip rests upon the 
cylinder a small plate of platinum is fastened, and the opposite 
end of the strip is attached to the centre of a diaphragm of mica, 
four inches in diameter, firmly fixed to the framing of the instru- 
ment by its circumference. By connecting the strip to the zinc 
element of a voltaic battery, and the chalk cylinder to the copper 
pole, and rotating the cylinder at a uniform speed away from the 
diaphragm, it will be found that, when no current is passing, the 
friction between the moistened surface of the chalk and the 
platinum strip is sufficient to drag the centre of the diaphragm 
inwards, and it will take up a fixed position of equilibrium when 
the frictional pull in the centre of the diaphragm is equal to the 
elastic tension of the strained diaphragm. The moment, how- 
ever, that an eleCtric current is allowed to pass between the strip 
and the cylinder, eleCtro-chemical decomposition takes place, 
the friction between them is reduced, and the diaphragm, finding 
its elastic tension unopposed, flies back to a second position of 
equilibrium dependent upon similar conditions ; and, if a variable 
or undulatory current of electricity be transmitted through the 
instrument, the diaphragm will be kept in continual motion by 
the constantly varying friCtion existing between the chalk and 
the platinum dragging the diaphragm in opposition to its own 
constant elastic tension. So marvellously sensitive is this simple 
mechanical arrangement to the smallest as well as to the most 
rapid and complicated variations in eleCtrical intensity taking 
place in the transmitted current, that all the complex sonorous 
undulations propagated by human articulation instantly produce 
their corresponding variations of frictional resistance, and 
the diaphragm reproduces, in a loud voice, the words which 
are being uttered into the telephone at the distant station. 
The cause of the superiority in power of this instrument over 
others must be looked for in the fadt that the vibration of the 
diaphragm is produced, not as in other telephones by an eledtric 
current, but by local mechanical means, that is to say, by the 
rotation of the cylinder by hand, by clock-work, or by any other 
motive power. The function of the eledtric current is purely a 
controlling and regulating one ; it determines how much or how 
