Final answer:
Without further context, it is impossible to determine if the deviation increases or decreases when the glancing angle is twice the reflected angle; more information about specific angle definitions and relationships is required.
Step-by-step explanation:
If the glancing angle is twice the reflected angle, the deviation either increases or decreases depending on the relationship between the angles. However, without additional context or information, it's impossible to determine whether the deviation explicitly increases or decreases as this would depend on the specific geometry and definitions of the angles involved in the problem. For instance, in geometric optics, the angle of deviation depends on the angle of incidence and the angle of reflection. If the 'glancing angle' refers to the angle of incidence, and it is twice the angle of reflection, this may not provide enough information to conclude how the deviation changes. It would be essential to compare the initial and final angles of incidence and reflection to determine how the deviation changes.