246 THE BIOPHYSICAL PROBLEM OF NERVE CONDUCTION 



If a difference of potential is now applied to the deflection plates 

 marked y, a movement of the spot will take place from A to B Y , or from 

 A to C Y , depending on whether the upper plate is positively or negatively 

 charged. A similar explanation applies to the movement of the spot on 

 the X axis which is due to the position of the vertical deflection plates 

 marked x. 



Deflection voltage ? R f ?R<? Sweep circuit 



K 



ie ? R f <?R? 



y x 



■± 



rt=s^^=H4»g 



-1500, , 



-1125 



D-c 



supply 



+ 



Fig. VI-20. The essential elements of a high-vacuum cathode-ray oscillograph 

 tube. Electrons are emitted from the indirectly heated oxide-coated cathode K. 

 Internal tungsten heater element / wound non-inductively. GA\A% are the elements 

 of an electron lens (see electron microscope). G, the grid, a nickel cylinder with 

 small hole, controls intensity of beam. A\, used to collimate the beam, is the first 

 anode or focusing electrode. A%, the second anode, accelerates the electrons toward 

 the screen. By varying its voltage, spot size and intensity may be regulated. P, 

 the postaccelerating electrode (A. B. DuMont Laboratories, Inc.) or intensifier of the 

 luminous spot. It is a conducting ring placed on the innerside of the glass. The 

 potential between this electrode and A? is approximately equal to that between A<? 4 

 and K. In order to avoid a loss in sensitivity due to P the anode Ai is connected 

 to the static internal shield. R is 1 megohm. Overall length with a 20-cm screen 

 is about 55 cm. 



Suppose both the x and y plates to be charged electrically positive, and 

 to the same potential, at the same time. Then the spot will move along 

 the diagonal from A to D. Upon reversal of the polarity of the plates, 

 the spot will move from A to D' . 



If, for example, a sinusoidally varying voltage, such as the 60-cycle 

 lighting source, is impressed on the x plates, the spot will move rapidly 

 back and forth with simple harmonic motion to produce a horizontal 

 fluorescent trace, the half length or amplitude of which is proportional 

 to the voltage. A similar trace along the Y axis will be obtained if the 

 same voltage is attached to the y plates. If the same alternating poten- 

 tial is connected to both the x plates and the y plates, the resultant 

 pattern will be a straight line inclined at 45° as DAD'. The fluorescent 

 spot moves along this line as in simple harmonic motion, indicating that 

 these two potentials are in phase. If the magnitude of the two deflec- 



