Our Troy pound, while taking its name, like the Scots and Dutch pound, from the Troyes marc, took its standard from some pound of full weight, possibly from the Bremen pound, introduced by the Hanse merchants. Its exact standard appears due to the influence of the averdepois pound, and this would explain—
How the Averdepois Pound was of 7000 Grains.
This division into 7000 grains was not arbitrary, but it was due to the desire to give it as simple a ratio as possible to the new Troy pound. It was found by a Parliamentary Committee in 1758 to weigh 7000 of those grains into which the Troy pound had always been divided, necessarily into 5760 of them (12 oz. × 20 dwt. × 24 grs.). Now it seems probable that when the Troy pound was adopted for mint purposes its weight might be modified, on the advice of goldsmiths and merchants, so as to give it a convenient relation to the old-established averdepois pound. Supposing the new pound were of the Bremen standard, 7693 grains, of which 12 ounces = 5769·6 grains, then its weight would be to that of averdepois as 5769·6 to 7000, or as 5760 to 6987·8. To make the proportion 5760 to 7000 it would be necessary to decrease the weight of the Troy pound by about 8 grains or to increase that of the averdepois pound by about 10 grains. It is probable that the latter alternative was adopted, and that the averdepois pound was raised in such proportion that it now weighed 7000 grains of the Troy pound = 5760 grains. This accounts for the rise in the weight of the averdepois standard between Plantagenet and Elizabethan times, making the ounce = 437-1/2 grains instead of the 437 grains of the Roman ounce.
It is not improbable that the change of mint-standard from Tower to Troy was due to the very inconvenient ratio of the Tower pound to the averdepois pound. The mint-pound being necessarily divided into 12 ounces of 20 pennyweight of 24 parts or grains = 5760 parts, the ratio of the Tower and averdepois pounds was 5400 to nearly 7000, or 5760 : 7453, the latter figure being about the number of Tower grains = 0·937 grain, contained in the original averdepois pound. The introduction of a new pound, which by slight modification in either it or the averdepois pound would give the simpler ratio of 5760 to 7000, would probably be most welcome to the mercantile community.
In Teutonic countries the usual system of dividing the pounds was as follows:
| Mint-marc of 8 oz. × 20 dwt. × 24 grs. (or 32 azen). Oz. of 480 grains. | |
| Medicinal lb. of 12 oz. × 24 scruples × 20 grs. Oz. of 480 grains. | |
| Commercial | ⎧ Marc of 16 loth × 16 ort (German). |
| ⎩ lb. of 16 oz. × 16 drams (English). | |
The Latin nations followed the ancient Roman system of dividing the ounce:
Mint-pound of 12 oz. × 6 sextulæ × 24 siliquæ = 1728 siliquæ, the ounce being of 6 × 24 = 144 siliquæ or carats, and the carat of 4 grains, giving 576 grains in an ounce.
| Medicinal lb. of 12 oz. | ⎧ × 8 drachmæ × 3 scrupuli × 24 granæ, |
| ⎩ × 8 drachmæ × 3 scrupuli × 2 oboli × 12 granæ. |
In Southern France: