1891 - 92 .] Dr W. Peddie on Transformation of Energy. 259 
the vapour in contact with a plane surface and a spherical surface of 
radius C. This result was first given by Lord Kelvin. 
VII. Induced Electromotive Forces . — Consider two circuits in 
which electric currents of intensities i and j respectively circulate 
similarly. Let the coefficient of mutual induction be M, and let us 
take as an experimental result the expression 
for the force / which tends to produce a displacement dx. If I and 
J are the electromotive forces acting in the circuits, we have 
fdx = id{jM) = dl . idt 
Similarly, 
