494 DE. J. HOPKINS ON ON THE KESIDUAL CHAEGE OE THE LEYDEN JAE. 
subsequent readings of the same series showed a steady decrease to as little as 15 per cent. 
The experiment was repeated with the same flask, but with shorter periods of discharge 
and with a similar result. 
6. Although the above view is only proposed as a provisional working hypothesis, 
some suggestions which it indicates may be pointed out. 
Temperature has three effects on the magnetic state of iron or steel : — (1) Changes of 
temperature cause temporary changes in the intensity of a magnet ; (2) temperature 
affects the “ permeability ” of a magnet ; at a red heat iron is no longer sensibly magnetic ; 
(3) a rise of temperature reduces coercive force. 
It may be expected that the polarity of dielectrics may also be affected in three 
analogous ways: — (1) a sudden change of temperature might directly and suddenly 
affect the polarity (an example of this we have in the phenomena of pyro-electricity) ; 
(2) the constant expressing the ratio of limiting polarity to electromotive force may 
depend on temperature ; and (3) temperature may alter the constant, expressing the rate 
at which polarity approaches its limiting value for a given force, as it is known to alter 
the specific conductivity. Mr. Perry’s experiments show that temperature does affect 
the polarization of dielectrics, but in which way does not appear. 
Sir William Thomson (papers on Electrostatics and Magnetism, art. 43) explains 
specific inductive capacity by a polarization of the dielectric following the same formal 
laws as magnetism. It is only necessary to introduce time into that explanation as here 
proposed to enable it to cover the phenomena of residual charge. Again (see Nichol’s 
Cyclopaedia), Sir W. Thomson explains the phenomena of pyro-electricity by supposing 
that every part of the crystal of tourmaline is electropolar, that temperature changes 
the intensity of its polarity, and that this polarity is masked by a surface distribution of 
electricity supplied by conduction over the surface or otherwise. We have, then, in 
tourmaline an analogue to a rigidly magnetized body, in glass or other dielectrics 
analogues to irop. having more or less coercive force. 
