RELIVS IN THE HULL SYSTEM 



11 



and was first used in the rommoii l)attt.'r\- board installi'd in Wor- 

 cester, Mass., in 1S9G. 



This relay consists of a tul)ular ni.ii;ncl with an iron disc arnialuri' 

 in the form of a truncated cone. This disc is brought to an (.diic 

 at its periphery and rests in an annular groove in the cap. \\'lu-n 

 the armature operates, it closes against an insulated contact stud 



G-No 15 Induction Col 



H- Common talking batLery. 

 I ~ Cleahnq-out signals . 



L~An&vyerinq plug. 

 M-Clearinq plug 



Fig. S — Early common liattciy cord circuit 



projecting from the core and when released drops away from the 

 core by gravity and rests against a stud projecting from the end of 

 the cap which provides the adjusting means for rfgulating the arma- 

 ture air gap. As the contacts of this relay were enclosed in the case, 

 the\' were protected from dust and this arrangement proved so desir- 





Fig. 6 — Early line relay 



able that it has been an accepted feature of nearly all relay designs 

 that have followed. This arrangement had the disadvantage, how- 

 ever, of not providing a means for determining the value of the 

 armature air gap or the contact separation. This condition was im- 

 proved in the next design which is shown in Fig. 7 by making the 

 cap longer and associating the armature with the magnet structure 



