[Footnote d: Dr and St. 1. 10.] THE customs of London differ from all others in point of trial: for, if the existence of the custom be brought in question, it shall not be tried by a jury, but by certificate from the lord mayor and aldermen by the mouth of their recorder[e]; unless it be such a custom as the corporation is itself interested in, as a right of taking toll, &c, for then the law permits them not to certify on their own behalf[f]. [Footnote e: Cro. Car. 516.] [Footnote f: Hob. 85.] WHEN a custom is actually proved to exist, the next enquiry is into the legality of it; for if it is not a good custom it ought to be no longer used. "_Malus usus abolendus est_" is an established maxim of the law[g]. To make a particular custom good, the following are necessary requisites. [Footnote g: Litt. Sec. 212. 4 Inst. 274.] 1. THAT it have been used so long, that the memory of man runneth not to the contrary. So that if any one can shew the beginning of it, it is no good custom. For which reason no custom can prevail against an express act of parliament; since the statute itself is a proof of a time when such a custom did not exist[h]. [Footnote h: Co. Litt. 113 _b._] 2. IT must have been _continued_. Any interruption would cause a temporary ceasing: the revival gives it a new beginning, which will be within time of memory, and thereupon the custom will be void. But this must be understood with regard to an interruption of the _right_; for an interruption of the _possession_ only, for ten or twenty years, will not destroy the custom[i]. As if I have a right of way by custom over another's field, the custom is not destroyed, though I do not pass over it for ten years; it only becomes more difficult to prove: but if the _right_ be any how discontinued for a day, the custom is quite at an end. [Footnote i: Co. Litt. 114 _b._] 3. IT must have been _peaceable_, and acquiesced in; not subject to contention and dispute[k]. For as customs owe their original to common consent, their being immemorially disputed either at law or otherwise is a proof that such consent was wanting. [Footnote k: Co. Litt. 114.]