488 PHILOSOPHICAL TRANSACTIONS. [ANNOI76O. 



and seems to have been the first that compared the original figures on the mo- 

 numents of Cossutius and Statilius with a modern standard. This he did with 

 such care and diligence, that his measures deserve a particular examination. 



The London foot, which he used on this occasion, was taken from the iron 

 standard of 3 feet in the Guild-hall, London ; which having been long since lost 

 or destroyed, we have nothing left to discover its true magnitude but the mea- 

 sures others have taken of it, and those which have since been taken of such 

 magnitudes as Greaves had compared with his copy of it. 



Snellius, from a measure sent him of this iron standard, determined the pro- 

 portion of the Rhynland to the London foot, as 1000 to 968. The Rhynland 

 foot, according to Picard, contains 696 such parts as the Paris foot contains 7 20: 

 whence the proportion of the latter to this measure from the iron standard, is as 

 1065.4 to 997 nearly. Eisenschmid found the Rhynland foot to contain 1 39 1.3 

 such parts as the Paris foot contains 1440; which gives 1065.4 to less than 9964-, 

 for the proportion of the Paris foot to that of the iron standard. Huyghens 

 makes the Paris to the Rhynland foot as 144 to 139; whence the proportion of 

 the former to Snellius's London foot, will be nearly as 1065.4 to 995^. But 

 there is reason to believe that Huyghen's measure of the Rhynland foot was 

 too small. By these comparisons it appears that Snellius's measure of tlie Lon- 

 don foot, from this iron standard, was at least 3 parts in 1000 shorter than 

 Graham's London foot. 



Our countryman Norwood, in l635, measured the distance between London 

 and York, in order to determine the length of a degree on the meridian ; which 

 he found to contain 367 1 96 London feet of this iron standard. The French 

 found the measure of a degree in the latitude 66° 20', to be 57438 toises, and 

 at the equator 56783. Hence the measure of a degree in 52^ 44' (the middle 

 latitude between London and York) will be found to be 57276 toises, or 343656 

 Paris feet. These numbers give the proportion of the Paris foot to that of the 

 iron standard, as 1065.4 to 997-1 — , wanting somewhat less than 3 parts in 

 1000 of Graham's London foot. 



Picard's paper De Mensuris, and another on the same subject by Auzout, 

 printed with it, contain some measures which Greaves had before compared 

 with his London foot. Both these papers were written after the renewal of the 

 standard of the Chatelet in 1668. The former is so full of inacuracies and mis- 

 takes, that little use can be made of it; but Auzout's measures appear to be ac- 

 curate ; and as he seems to have taken his Paris foot from the toise in the 

 Chatelet for this purpose, it was probably a correct measure of that standard. 



Such of his measures as answer to Greaves's, are here reduced to thousandth 

 parts of the London foot, reckoning his Paris foot to contain 1065.4 such parts. 



