THE ELECTRIC TELEGRAPH. 



fig. 17, upon which two projecting rings are raised in the 

 groove between which the wire is wrapped. This glass knob 



Fig. 17 



attached to an iron shank 





as represented in fig. 18, which 

 is driven into the post. 



Another form of support 

 used on these lines is repre- 

 sented in fig. 19, which consists 

 of two rectangular blocks of 

 glass, in each of which is a semi- 



cylindrical groove corresponding with the thickness of the con- 

 ducting wire, so that the wire being laid in the groove of one 

 of them, and the other being laid upon it, will be completely 

 enclosed within the block of glass produced by 

 their union. These blocks of glass are surrounded 

 and protected by a larger block of wood, as repre- 

 sented in the figure, where the white part represents 

 the glass, and the shaded part the wood. 



The supports are sometimes attached to the sides 

 of the posts, and sometimes placed upon an hori- 

 zontal cross bar, as represented in fig. 20. 



Fig. 20. 



Fig. 19. 



The supports used in House's lines consist of a glass cnp about 

 five inches in length and four inches in diameter, having a 

 coarse screw-like surface cut inside and out. This glass cap 

 (2) fig. 21 is screwed and cemented into a bell - shaped iron 

 cap (1) from three to four pounds, in weight, projecting an 

 inch below the lower edge of the glass, protecting it from 

 being broken; this is fitted with much care to the top of 

 140 



