324 BELL SYSTEM TECHNICAL JOURNAL 



SO that in equation (3.25) 



gi = 32°\6' + 3°28.7' = 35°44.7' 

 Similarly 



^2 = 32°7' + 6°30' = 38°37' 



g3 = 32°16' - 3°28.7' = 28°47.3 



g4 = 32°7' - 6°30' = 25°37' 



In the case (d) of an atomic plane which intersects the plate face in a 

 line which is neither parallel nor normal to the plane of the instrument, the 

 angle 6 that the atomic normal makes with the plane of the instrument will 

 be different for different positions of the plate. 



If Nv is the direction cosine of the normal to the atomic plane with 

 reference to that plate edge (P axis) that is placed in the vertical position, 



d = cos-Wv^ - 90° = - &m-'Nv 



This value of 5 may be used in determining jS according to formula (3.3). 

 For example, when the P3 axis (width) of an NT plate is placed parallel 

 to the axis of the instrument, 



5 ^ -sin-i.Vs = -sin-i .060293 = -3°27.4' 



(The negative sign indicates deflection of the normal toward the negative 

 end of the P3 axis and may be disregarded in determination of (3). 



Whence sin /3 = 2 sin 32°03' sin 3°27.4' 



(3 = 3°40' 



This means that the beam reflected from the (2l-3) atomic plane when 

 the NT plate is placed with its P3 (width) axis parallel to the axis of the 

 instrument would be received by an ionization chamber which would accept 

 a beam making an angle of 3°40' with the plane of the instrument. 



When the Pi axis (length) of an NT plate is placed parallel to the axis 

 of the instrument 



8 = cos-Wi - 90° = sin-i -.11223 = -6°26.7' 



Since this is a larger /3 value than most ionization chambers will accept, 

 the (2l-3) plane cannot be used in most cases to check an NT plate with 

 its Pi axis parallel to the axis of the instrument unless the ionization chamber 

 is moved vertically. 



(b) and (c) Atomic plane intersecting plate-face in a line which is either 

 normal or parallel to the plane of the instrument. 



For plates rotated about X only (as AT, BT, CT and DT) the problem 



