The practicability of causing it arbitrarily to change its processes at any moment, on the occurrence of any specified contingency (of which its substitution of (\frac{1}{2}\cos\overline{n+1}\theta+\frac{1}{2}\cos\overline{n-1}\theta) for (\cos n\theta\cdot\cos\theta), explained in Note E., is in some degree an illustration), at once secures this point.