The wey or weigh became, in statute French, poids, pois; but the scribes took the wrong pois and thinking it meant ‘pease’ made it pisa in their Latin, just as they took the wrong ‘nail’ and made it L. clavus, and in French clau, through L. clavis, meaning a ‘key.’
Lead Weight
While the fother is 17-2/3 cwt. for coal, it is 19-1/2 cwt. = 2184 lb. for lead. This peculiar unit, also called the char or load, is the consequence of a statute 31 Edw. I, perhaps the most confused and bewildering of the many confused medieval statutes on weights and measures, and one in which subsequent interpolations may be suspected. It ordered two stones, one of 12 lb. and another of 12-1/2 lb., and to keep up the pretence of there being no weight other than of Tower standard, it declared that a pound shall contain 25 shillings. This shilling standard may be put aside.
The 12 lb. stone is ordered apparently either as a double of a customary ‘lead-pound’ of 6 lb. or to make the customary fotmal or ‘pig’ of lead, 70 lb. weight, ‘contain 6 stones (of 12 lb.) less 2 lb.’ It also says that the deduction of 2 lb. leaves ‘70 lb. making 5 stones.’ This passage appears to be a subsequent interpolation after the institution of Edward III’s 14 lb. stone.
The fother of lead, of 30 fotmals, would thus be = 2100 lb. But the stone of 12-1/2 lb., evidently intended to be 1/8 of the true hundredweight, and to pave the way for the coming 14 lb. stone, is also applied to lead. How it is not said; but the present fother, = 2184 lb., is almost exactly equal to 30 fotmal, each of 73 lb. = 2190 lb.; and 73 lb. is just 6 stone of 12-1/2 lb. less 2 lb.
The 70 lb. fotmal seems to have disappeared by the seventeenth century, but in the meantime the uncertainty of the fother led to the use of Boole-weight, meaning the weight used at the lead-boles or natural bowls in which lead ore was smelted. The fother, boole-weight, was 30 fotmals of 6 stone of 14 lb. Sometimes it was of 24 fotmals = 2016 lb., that is 18 cwt.
The meaning of Fother is given in [Chapter XX].
6. Trade-units of Weight
It is unnecessary to describe or even name the various weights peculiar to trade or local custom. Everyone in the trade knows them; out of it no one need know them. If a person not in the trade buys a cask of wine, a barrel of beer, a sack of flour or a load of potatoes, commonsense prompts him to ask how many gallons or pounds are contained in these units. It is the same in France and other countries of the metric system, where the cask, the sack, the churnful, &c., are trade-units with their peculiar equivalents of litres or kilogrammes. It is indeed by the use of trade-units that manufacturers evade the rigour of the metric system.