COMPARATIVE METROLOGY. 389 



kind in favour of 5 cubits ; and, considered apart from any such 

 reason, 10,000 cubits would be a more natural unit than 5000. 

 And this would give the league which occurs in modern times. 

 Let it be granted, however, that the Gallo-Roman league contains 

 as many cubits as the mile feet, it would immediately suggest 

 itself by analogy that the unit of square measure should be a 

 square whose side was 120 cubits, so as to correspond to the 

 actus. Thus we are led to the Arpentum, which continued to 

 be the unit of French surveying untij. the revolution, varied how- 

 ever in size by the difference between the French and the Ko- 

 man foot. Like the actus it is described as a square, the side 

 being of course 180 feet or 10 perches of 18 feet each. This was 

 known as the " Arpent de Paris," but there existed another also 

 much used called the " Arpent des Eaux et F6rets," connected 

 with the former by an approximately simple relation, but perhaps 

 resulting from a tradition of the old jugerum which must have 

 long survived in Provence. At least with the double jugerum it 

 coincides more closely than the pezza with the jugerum. This 

 latter arpent is a square of 220 feet, and therefore differs Less than 

 a half per cent, from being to the Arpent de Paris as 3 to 2, a 

 circumstance which may have modified its definition. Half of it 

 would be 24200 square feet, which would be precisely the juge- 

 rum if the Eoman foot were 132 Paris lines. The calculation in 

 Niebiihr's letter to Savigny implies a greater value than this of 

 the Roman foot, but there is no occasion to have recourse to any- 

 thing doubtful in order to show how nearly the two things coin- 

 cide. For if we take Gagnazzi's value already mentioned, the 

 jugerum will not fall short of the half Arpent des Eaux et Fdrets, 

 much more than one per cent. Two things are worthy of notice 

 respecting this second arpent. One, that it appears to have led 

 to a definition of the league as 60 times the side of the arpent, or 

 2200 toises ; the other, that there can be little doubt of its being 

 the origin of the Scotch acre, with which its coincidence in size 

 may be called absolute. Converting this arpent into yards, 

 according to the logarithms given in Babbage's Constants, I 

 make it a fraction more than 6108 square yards, the normal 

 Scotch acre being 6104 yards, though it is said to vary in dif- 

 ferent counties from 6084 to 6150 yards. Thus, if my fancies 

 (for I can hardly call them more) are right, we have the pezza 

 equal to two actus, the English acre to three, the Scotch to four, 



