QUARTZ CRYSTAL PLATES 



521 



crystals frequently have two high-frequency modes of vibration within 

 a kilocycle or so of each other and will start on either of these modes if 

 the circuit constants are changed slightly. These two modes usually 

 have widely different characteristics. 



600 



500 



iij 400 



200 



12 3 4 5 6 



THICKNESS — MM. 



'ig. 4 — The wave-length at which a 2.5 cm. square_ parallel cut crystal plate will 

 operate in an oscillator circuit as its thickness is progressively reduced. 



Apart from this seemingly erratic variation it has been the experience 

 of this laboratory that the parallel cut crystal will oscillate more 

 readily in the Pierce type of oscillator circuit. For this reason this 

 type of crystal has been used for a number of purposes and these 

 observed variations have been the object of considerable study. 



As a result of this work an explanation has been evolved to account 



