In the insane mind, these parentheses of reason, have been technically denominated a lucid interval, which in a former work[102:A] I have endeavoured to explain, as far as such state becomes obvious to the medical practitioner. Its legal force I do not pretend to calculate. According to the legal interpretation of a lunatic, he ought, in common justice, at those bright periods when he possesses an _extremely sound mind_, to be lawfully allowed the free and valid exercise of his volition. But having noticed in the work above mentioned that the term _interval_ is extremely indefinite, as applied both to time and space, it is the province of the law to define its duration and extent. As a constant observer of this disease for more than twenty-five years, I cannot affirm that the lunatics with whom I have had daily intercourse, have manifested these alternations of insanity and reason. They may at intervals become more tranquil, and less disposed to obtrude their distempered fancies into notice. For a time their minds may be less active, and the succession of their thoughts consequently more deliberate;—they may endeavour to effect some desirable purpose, and artfully conceal their real opinions, but they have not abandoned or renounced their distempered notions. It is as unnecessary to repeat that a few coherent sentences do not constitute the sanity of the intellect, as that the sounding of one or two notes of a keyed instrument, could ascertain it to be in tune. To establish its sanity it must be assayed by different tests, and it must be detected to be as lucid on the subject of those delusions, which constituted its insanity, as on topics of a trivial nature. But the law alone must determine whether it will consider an individual sane act as a lucid interval, and infer soundness of _mind_, which is the abstract term for all the intellectual phenomena, and implies the aggregate of the ideas, of the individual, from a single and successful effort. [102:A] Vide Observations on Madness and Melancholy pages 44 and 210.