W. P. White — Switch for Thermoelement Work. 313 



high. They are fastened to the celluloid tongues by small-headed 

 pins above and below the level of the bus bar. Their function 

 is to insure that the pressure of the operating pin shall be shared 

 by both copper strips. These bus bars are so located that when 

 any operating pin is pushed in and locked, the bars are pushed 

 back 2 mm , straining one or both of two stiff springs. Suitable 

 springs are obtained by mounting two spring clothespins at the 

 places shown in figs. 2a and b, and in the manner shown in fig. 3, 

 so that they are opened when the bus bars are pushed back. The 



Fig. 3. 



Thermoelement 

 bus bars 



Fig. 3. Detail of thermoelement connecting system from fig. 2, b. The 

 pin P 4 is tight in the bits bar support, and passes very loosely through one 

 side of the clothespin, to press against the other side. It prevents the 

 clothespin from sliding off the horizontal steel pins P 6 and P 6 . By pushing 

 the bus bars to the left the clothespin can be removed. Scale, "4 full size. 



strip of wood E, carrying the thermoelement leads, is so located 

 that the leads, when released, are 6 mra from the bus bars. 



The two movable auxiliary -connecting frames, X t and X 2 , fig. 

 2, are intended to make connection with the appropriate aux- 

 iliary apparatus (usually, potentiometer dials) when any one of 

 the thermoelements (or other " unknowns ") is connected. Each 

 is made with a 5/16 inch (8 mm ) mild steel rod 28 0m long, driven 

 with a very tight tit through two strips of wood, one 20 nim square 

 and 12 cm long, the other 6-5 cm wide, 20 cm long and 18 mm thick. 

 The square strip carries 4 copper strips (fastened and insulated 

 by celluloid, as usual) which are connected to a set of 4 poten- 

 tiometer switches. The broader strip of wood is pressed by the 

 pins P„ of the operating rods. The steel rod does not pass 

 through the wood midway of its thickness. In the lower frame, 

 the top of the broad strip must be i2' Qm below the center line of 

 the operating pins, while the top of the 20 mm strip must be i7 mm 

 below. Hence the steel rod is 5 mm lower in the broad bar than in 

 the narrow one. In the upper frame, the broad strip must be 



