Bauhaus-Universität Weimar

CONTINUOUS-RECORDING PENS 
J. H. THOMPSON and A. T. WILSON 
Department of Physiology, Middlesex Hospital, Medical School, London 
Received for publication February 16, 1930 
The disadvantages found by the older workers in using ink- 
filled pens for writing on recording surfaces were associated with 
the large amount of friction between the pen and the paper, viz., 
failure to record small movements, marked diminution in all 
other movements, particularly rapid ones, and a poor tracing due 
mainly to an inadequate and discontinuous flow of ink. Con¬ 
sequently, smoked paper came into general use as a recording 
surface, in spite of its obvious disadvantages. 
In working with the Thompson sphygmanograph (1) we found 
the disadvantages to be a great hindrance/ especially when 
continuous records taken over a period of an hour or more were 
required. Attention was therefore directed to the evolution of 
some other means of recording. It was essential that the appara¬ 
tus should possess the following properties: (a) Simplicity; 
(6) faithful recording of all excursions of the float; (c) formation 
of a good tracing. Experiments were first of all conducted, using 
paper impregnated with potassium iodide and starch in suitable 
proportions, the drum upon which the paper was wound being 
connected to one pole of a small battery, the other pole being 
attached to a fine wire suspended vertically which was in contact 
with a small piece of platinum wire fused into the stem of the 
glass float, and which therefore served the double purpose of 
making electrical contact and keeping the platinum wire in 
position against the paper. The platinum wire was shaped to 
form a writing point. 
The apparatus fulfilled the three essential conditions stated 
above. It was found to be very efficient in recording rapid 
excursions of a lever—e.g., muscle twitches; but for the recording 
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