BALANCED POLAR MERCURY C()\TA( T KKI.W | K).", 



capillary reservoir which establishes a negative head in the nuMrnry 

 equal to that obtanied by the height of the contacts above the mercury 

 reservoir ni the switch shown in Fig. 2. To provide for the return of free 

 mercury to the reservoir, a wet strip of metal is placed along the glass 

 wall underneath the contacts. 



The capillary reservoir is essentially a bundle of tubes with walls wet 

 by the mercury. The amount of mercury in the switch is such that the 

 tubes are about half full. The mercury meniscii in these tubes are tangent 

 to the walls and therefore have a spherical surface with a radius equal to 

 that of the tubes. The proper tube radius (Ri = R. = 0.033 cm) for 



Fig. 10 — Horizontal relay. 



the desired negative head {h = 2.07 cm) is obtained from equation (3). 

 As the tubes have a uniform bore, the negative head which they estab- 

 lish is not critically dependent on the amount of mercury in them. 



The capillary reservoir is made from thin strip, formed and then rolled 

 into a cylinder. It surrounds the metal tube and is welded to the base of 

 the armature. The drain element is sealed into the glass at one end, and, 

 at the other end, is held in contact with the capillary element by the 

 surface tension and negative head of the mercury. 



The horizontal switch is an experimental design and has not been put 

 into production. It can be assembled in the housing shown in Fig. 1 for 

 plug connection to a vertical panel. Fig. 10 shows a preliminary model 

 with the new type terminals for wrapped connections.^ It is adapted for 



2 Solderless Wrapped Connections, B.S.T.J., May, 1953. 



