680 KANSAS CITY REVIEW OF SCIENCE. 
is well known in physics as the ‘‘axial electro-magnetic force,” and in it I found 
what I sought, namely—a combination of delicacy and strength in the proper 
proportions. A diagramatical illustration of its application may be seen in fig. 6, 
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Ee 
UC 
Hi) 
ML 3 
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where H represents a helix of peculiar construction applied to the purpose in 
hand; C is a soft iron tube in connection with the short end of the lever (L); P 
represents the movable surface or strip of paper; F, the fulcrum of the lever, 
and EH its marker or stylus; T, the thermometer proper introduced into the circuit ; 
X, the battery; c, the curve, and S, the brass drum over which the strip of paper 
(P) moves. ; 
Having comprehended the principles, the action of this combination is obvi- 
ous. If an electric current passes through the helix (H), the core (C) will be 
drawn into said helix, carrying with it the short end of the lever (L), to which it 
is attached. This movement naturally causes the marking end of the lever to 
make a still longer excursion in the opposite direction. Upon breaking the 
circuit, the attractive power of the helix is abolished, and the counter-action of 
the spring (s) returns the lever to its normal position. 
The depth to which the core (C) is drawn into the helix (H) being dependent 
upon the strength of the current passing through the coils of wire, the excursions 
of the tracer or lever will also be great or small, according as the current is weak 
or strong. 
The lever (L) is delicately made, and its fulcrum provided with jewel mount- 
ings. Its short end is connected with the core (C) by means of a universal joint, 
while its longer end has inserted in it asilver stylus reaching to the surface of the 
traveling paper. ‘The latter moves over a brass drum forming a portion of the 
