343 Mr. J. N. Hearder on a New Form of Telegraph Cable 



If a Leyden jar or a coated glass plate have layers of paper 

 or any other fibrous material inserted between either or both of 

 its coatings and the glass, although the glass may, as far as the 

 ph?enomena of tension or attraction are concerned, be charged to 

 the same intensity, yet the effects of the discharge suffer an 

 extraordinary diminution, as will appear by the following expe- 

 riments. (Coated glass plates afforded the most ready means of 

 carrying out this inquiry, and were consequently employed for 

 the purpose. The effects of the discharge were examined by 

 means of the thermo-electrometer before described.) 



1st. To ascertain the effect of interposing porous media be- 

 tween the glass and its coatings, various substances were em- 

 ployed, such as silk, flannel, calico, paper, &c. The effect of the 

 discharge from the glass plate, with its two ordinary tinfoil 

 coatings, was first ascertained by the thermo-electrometer; the 

 tinfoil coatings were then removed, and the several porous 

 substances were in turn placed upon the glass, varying from 

 1 to 3 layers in thickness, either on one or both sides of the 

 glass ; and, the coatings being carefully replaced upon them, 

 the glass was again charged, and the effects upon the elec- 

 trometer noticed. Without going into detail upon the results 

 of each modification of the arrangement, it may be sufficient to 

 state that, whilst with the ordinary tinfoil coatings a given 

 effect was produced, only y^^th to y^^th of the effect was 

 obtained when the porous layers were interposed; and this 

 diminution of effect bore no apparent relation to the conduct- 

 ing or non-conducting character of these media. 



In order to ascertain if these losses were occasioned by the 

 greater distance to which the tinfoil coatings were removed, 

 glass plates of a thickness corresponding to the united thickness 

 of the glass plates and fibrous coatings before mentioned were 

 employed, and coated with tinfoil in contact with the glass ; 

 but these gave results bearing their correct relation to the differ- 

 ence in the thickness of glass when coated with tinfoil alone, the 

 residts being very much higher than those obtained by the inter- 

 vention of the porous media. The quantity of electricity thrown 

 on as charge was accui'ately measured in each experiment, and 

 the discharging interval was retained the same. 



Thus the tension underwent no change; the intensity, as 

 evidenced by attraction, was more rather than less ; and yet the 

 thermometric corresponding to the galvanometric effects in 

 wires suffered this extraordinary diminution. 



Again, the arrangement was modified by using two plates of 

 glass placed upon each other as a double dielectric ; tinfoil coat- 

 ings were placed upon the two outer surfaces, and porous layers 

 inserted between the plates. The reduction of effect was here 



