ALL SUBSTANCES ELECTRIC. 197 



amber, resins, sulphur, and glass, exhibiting more power- 

 fully the phenomena of frictional or mechanical elec- 

 tricity, than the metals, charcoal, or plumbago. Solid 

 bodies allow this peculiar principle to pass along them 

 also in very different degrees. Thus electricity travels 

 readily through copper and most other metals, platinum 

 being the worst metallic conductor. It also passes 

 through living animals and vegetables, smoke, vapour, 

 rarified air, and moist earth ; but it is obstructed by 

 resins and glass, paper when dry, oils, and dry metallic 

 oxides, and in a very powerful manner by Gutta Percha.* 



* " A good piece of gutta percha will insulate as well as an equal 

 piece of shell-lac, whether it be in the form of sheet, or rod, or fila- 

 ment; but being tough and flexible when cold, as well as soft 

 when hot, it will serve better than shell-lac in many cases where 

 the brittleness of the latter is an inconvenience. Thus it makes 

 very good handles for carriers of electricity in experiments on 

 induction ; not being liable to fracture in the form of thin band or 

 string, it makes an excellent insulating suspender; a piece of it in 

 sheet makes a most convenient insulating basis for anything 

 placed on it. It forms excellent insulating plugs for the stems of 

 gold-leaf electrometers, when they pass through sheltering tubes, 

 and larger plugs form good insulating feet for electrical arrange- 

 ments; cylinders of it, half an inch or more in diameter, have 

 great stiffness, and form excellent insulating pillars. In these 

 and in other ways its power as an insulator may be useful." 

 On the use of Gutla Percha in Electrical Insulation : by Dr. 

 Faraday; Philosoph. Mag., March, 1848. 



The following deductions have been given by Faraday, in his 

 Researches in Electricity, a work of most extraordinary merit, 

 being one of the most perfect examples of fine inductive philo- 

 sophy which we possess in the English language : 



" All bodies conduct electricity in the same manner from 

 metals to lacs and gases, but in very different degrees. 



" Conducting power is in some bodies powerfully increased by 

 heat, and in others diminished, yet without one perceiving any 

 accompanying essential electrical difference, either in the bodies, 

 or in the change occasioned by the electricity conducted. 



"A numerous class of bodies insulating electricity of low 

 intensity, when solid, conduct it very freely when fluid, and are 

 then decomposed by it. 



" But there are many fluid bodies which do not sensibly con- 



