Electrolytic Theory of Dielectrics. 471 



Of course a theory which is to account for the cohesion 

 of pyro-electric crystals must also account for that of all 

 dielectrics. And in fact, according to the present view, 

 pvro-electric crystals only differ from other crystals in the 

 peculiar chain-like arrangement of their molecules, whereby 

 the cohesive force, as it were, shows itself externally ; whereas, 

 in the case of other substances, it is kept entirely within their 

 bounding surfaces. As regards the variations of tenacity 

 in different substances, they are, I think, to be easily accounted 

 for by the different sizes, masses, and perhaps shapes of the 

 molecules as compared with the charges they carry. Varia- 

 tions in these quantities will give rise to a greater or less degree 

 of pairing, as well as to alterations in d and in internal 

 pressure, sufficient to account for a greater range of variation 

 than is observed in the tenacity of homogeneous bodies. 

 (Porous substances like cement do not fall under this head, 

 of course. They may be regarded as containing an infinite 

 number of flaws, and their tenacity will therefore be too 

 small.) 



The chief difficulty is, however, met with in the case 

 of elementary substances. It is not easy to see where a want 

 of symmetry occurs in the combination of two like atoms, to 

 account for their being or becoming oppositely charged. The 

 question is a large one, and one which is intimately connected 

 with the manner of discharge of electricity through simple 

 gases. It is, for instance, uncertain whether the two atoms 

 of an oxygen molecule are oppositely charged to start with, or 

 become so by induction on entering a strong electrostatic 

 field. It is, however, extremely probable that after separation 

 they possess their ionic charge ; so that, unless there is a limit 

 to the capacity of an atom for having electricity induced on it, 

 the former view is perhaps the more likely. I merely mention 

 this to show that the existence of opposite charges in like 

 atoms is not a priori impossible. 



Specific Inductive Capacity and Dielectric Strength. 



Two other physical constants with which initial molecular 

 charges should be closely connected are those of Specific 

 Inductive Capacity and Dielectric Strength. From both 

 these quantities it is possible to obtain a value of g. 



Place the mixture of oppositely charged particles, discussed 

 under cohesion, in an electrostatic field. If the field is not 

 too strong there will be a slight movement of all the + par- 

 ticles in one direction and of the — particles in the opposite 

 direction. This will be equivalent to coating the surfaces of 

 the mixture at which the lines of force enter and leave it with 



