1A5

a)

b)

c)

Figurę 12.6. In (a)s_? = O for 4G. Wc can change a, in two ways: (b) if we till thc specimen thrrnigh anglc r\, thc row of spots moves insidc the sphere; (c) if wc tik the beam through r\ abovc thc spccimcn, in the oppo-site directioo, the sphere moves outside the row of spots.

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