INSULATORS . 
ii 7 
together with the circumstance that no part has to be fitted or 
cemented, combines to favour the duration of the insulator by 
removing the bad effect of variations of temperature. Since 
this form has been adopted in' Belgium, the breakage of 
insulators occurs only in cases of malicious injury or of quite 
exceptional accidents. 
2nd. The wire being free in the hook, and the stirrup having 
a certain amount of elasticity, the porcelain has only to bear 
Fig. 51. Fig. 52. 
the weight of the wire : it is not, like an insulator to which 
the wire is rigidly attached, subjected to sudden variations of 
strain, and to vibrations tending to loosen it. 
The internal hook is not so thick that its dilation would 
rupture the bell, as happens with certain forms adopted in 
Prussia. Now it is known that cracks in the supports are 
especially damaging to the insulation. It follows therefore 
that an insulator which on first setting up was superior to one 
on the Belgian system, might after some time become greatly 
