476 Dr. D. A. Keys on a Piezoelectric 



figure 2. It consists of a glass tube GG, the one end o£ 

 which is cemented by wax into the brass sleeve BB, which 

 in turn is soldered into the brass tube CC. The other end 

 o£ GG is fitted with a ground glass stopper AA, into which 

 two stout metal rods, ^\ inch in diameter, E and D are 

 sealed. To the ends o£ these rods is attached a fine tungsten 

 wire F, surrounded by a small concentrating cylinder H as 

 shown. The filament is wound in the form o£ a cylinder 



Fig-. 2. 



To crystals 



rtl— -#| 



"Vvv^*" 



of four or five turns and is heated to incandescence by the 

 8-volt storage battery I, which is connected in series with an 

 ammeter J and a regulating resistance K. The wbole 

 heating circuit is placed on an insulated platform. LL is a 

 brass guard tube j inch in diameter having a small hole 

 in the centre of one end. M and N are two insulated brass 

 condenser-plates 5 cm. long and 1 cm. wide, placed \ cm. 

 apart. They are connected to the leads P and Q which pass 

 through openings in LLand then through the glass tube GG 

 as shown. WW is an electromagnet wound, on a soft iron 

 laminated core and excited by a small alternating current of 

 known cycle. The current through WW is adjusted to the 

 proper strength by means of a variable resistance. B and K 

 are connected to an Evershed and Vignoles' high potential 

 direct current generator T supplying a constant potential 

 difference that may be varied from 8000 to 5000 volts, which 

 is measured with an electrostatic voltmeter. The photo- 

 graphic plate on which the motion of the cathode ray beam 

 is traced is 5 inches long by 1^ inches wide, and is placed in 

 a holder X with the film side exposed to the action of the 



