on certain Theoretical Opinions, 49 



17. In any case of the intermixture of opposite qualities, 

 may it not be said in the language which you employ, " the 

 moment we leave the element of perfection at one extremity, 

 we involve the element of perfection at the opposite"? Might 

 it not be said of light and darkness, or of opakeness and trans- 

 lucency ? in which case, to resort to your language again, it 

 might be added, " especially as we have not in nature, a case 

 of perfection at one extremity or the other." But if there be 

 not in nature any two bodies, of which one possesses the pro- 

 perty of perfectly resisting the passage of electricity, while the 

 other is endowed with the faculty of permitting its passage 

 without any resistance; does this affect the propriety of con- 

 sidering the qualities of insulation and conduction in the abs- 

 tract, as perfectly distinct, and inferring that so far as matter 

 may be endowed with the one property, it must be wanting 

 in the other ? 



18. Have you ever known electricity to pass through a 

 pane of sound glass ? My knowledge and experience create 

 an impression that a coated pane is never discharged through 

 the glass unless it be cracked or perforated. That the pro- 

 perty by which glass resists the passage of electricity, can be 

 confounded with that which enables a metallic wire to permit 

 of its transfer, agreeably to Wheatstone's experiments, with 

 a velocity greater than that of the solar rays, is to my mind 

 inconceivable. 



1 9. You infer that the residual charge of a battery arises 

 from the partial penetration of the glass by the opposite ex- 

 citements. But if glass be penetrable by electricity, why does 

 it not pass through it without a fracture or perforation ? 



20. According to your doctrine, induction consists " in a ' 

 forced state of polarization in contiguous rows of the particles 

 of the glass" (1300) ; and since this is propagated from one 

 side to the other, it must of course exist equally at all depths. 

 Yet the partial penetration suggested by you, supposes a col- 

 lateral affection of the same kind, extending only to a limited 

 depth. Is this consistent? Is it not more reasonable to sup- 

 pose that the air in the vicinity of the coating gradually re- 

 linquishes to it a portion of free electricity, conveyed into it 

 by what you call " convection" The coating being equally 

 in contact with the air and glass, it appears to me more easy 

 to conceive that the air might be penetrated by the excite- 

 ment, than the glass. 



21. In paragraph 1300, I observe the following statement: 

 " When a Ley den jar is charged, the particles of the glass are 



forced into this polarized and constrained condition by the 

 Phil Mag, S. 3. Vol. 17. No. 107. July 1840. E 



