Speaking generally, the state of idiotcy is well understood, although cases of an intricate nature may occasionally occur: but there is considerable probability, that the interpretation that has adhered to the term lunacy, more especially in the estimate of the lawyer, has been the source of considerable error, and has also tended to introduce the middle and undefined epithet of unsoundness. The old physicians, for whom modern practitioners entertain less reverence than lawyers feel for their predecessors, concurred, that lunatics were not only persons of disordered mind, but that their intellectual aberrations corresponded with certain changes of the moon: and this lunar hypothesis which had beguiled the medical profession, will furnish a sufficient apology for its adoption by the lawyer. It is a necessary consequence, if the moon, at certain periods, shed a baneful influence on the human intellect, that the intermediate periods would be exempt from its contamination; or, speaking more technically, at certain phases of that luminary, a person would be visited by an insane paroxysm, and at others, experience a lucid interval. The belief in these alternations of insanity and reason, is perspicuously stated in your Lordship's judgment of 1815, on the Portsmouth petition. "The question whether he was a lunatic, being a question admitting, in the solution of it, of a decision that imputed to him, at one time, an _extremely sound mind_, but at other times, an occurrence of insanity, with reference to which it was necessary to guard his person and his property by a commission issuing." Notwithstanding it must be admitted that "There are more things in heaven and earth Than are dreamt of in our philosophy;" yet, in the present times, our faith in the influence of the lunar aspects has considerably abated, and we employ the term lunatic as a familiar expression, to denote a person of insane mind, without any reference to its derivation, or supposed ascendency of the moon, which my own observations have tended to disprove:--but as the phrase lucid interval is, in its legal sense, connected with lunatic, some investigation of its meaning becomes absolutely necessary.