VOL. LXXXVIII.J PHILOSOPHICAL TRANSACTIONS. 305 



= the total length therefore 36.00130 inches, the thermo- 



— 0.00127 

 .00135 

 .00128 



meter at 60°.8. 



Mean = .00130. 

 The interval on the line marked Exch. was shorter than mine by 

 - .0066} 

 .0066 f 

 .0068 > = the total length = 35.9933 inches, the therm, at 6o°.6. 



.0067 J 

 And the Paris half-toise, which had been supposed by the Academy to be = 38.355 English inches, was 

 found, compared with mine, to be = 38.3561 1 



.3563 J- Mean = 38.3561 Inches.* 

 .3559 J 



The 1st of the preceding observations giving 36.0013") 



The 2d 35.9933 > Inches. 



The mean length of Mr. Graham's standard becomes 35.9973 J 



From the information in the report of a committee of the House of Commons, 



in 1758, I learnt that Mr. Bird's parliamentary standard had been in the custody 



of some of its officers, but of whom nobody knew: however, under the authority 



of the Speaker, who was so good as to furnish me with a room in his house, to 



make the comparisons in, I at last discovered this valuable original in the very safe 



keeping of Arthur Benson, Esq., Clerk of the Journals and Papers, and which I 



* Dr. Maskelyne says, this standard yard of Mr. Graham's was -p^ inch longer on 3 feet than Mr. 

 Bird's divided scale, which he generally made use of in all his operations of dividing ; and, from one 

 made conformably to this of Mr. Bird's, Mr. Troughton divided my scale of 60 inches. This remark 

 seems to agree with my 1st and 3d comparison, but not with the intermediate one. See Phil. Trans. 

 for 1768, p. 324. 



As I am now on the subject of foreign measure, it may not be quite out of place to say a word on 

 the length of the ancient Roman foot, which I am enabled to do with some precision. Some years 

 ago, when I was in Italy, I had several opportunities of ascertaining the length of this measure, by 

 actual examination of the Roman foot rules, of which I have met with 9, viz. 2 in the Capitol at 

 Rome ; 1 in the Vatican ; 5 in the Museum at Portici, near Naples ; and lastly, one in the British 

 Museum, sent from Naples by Sir William Hamilton. They were all of brass, except one half foot 

 of ivory, with a joint in the middle, resembling our common box or ivory rules : and, by reference to 

 my journal kept at that time, I find the mean result from all the 9 rules, viz. by taking both the whole 

 and the parts of each, (for they were divided into 12 inches, and also into l6ths, or digits), gave, for 

 the length of the old Roman foot, in English inches, correspondent to Mr. Bird's measure, = 11.6063. 

 In confirmation also of this conclusion, and agreeably to the idea of Mons. De La Condamine, in 

 the " Journal of his Tour to Italy," I took the dimensions of several ancient buidings, viz. the interior 

 diameter of the temple of Vesta ; the width of the arch of Severus 3 the door of the Pantheon ; and the 

 width of the base of the quadrilateral pyramid of Cestius, which, it is curious to observe, I found exactly 

 100 old Roman feet, and 125 feet high. This I do not remember to have seen noticed by any former 

 traveller. 



The mean result of these experiments gave me 1 1.6 17 English inches. 



Ditto, as before, from the rules 11 .606 ditto. 



The mean of the 2 modes of determination is 1 1 .612 ditto. 



I may add, that in the Capitol is a stone, of no very ancient date however, let into the wall, on which 

 is engraven the length of several measures, from which I took the following : The ancient Roman foot 

 = 11.635 English inches. The modern Roman palm, = 8.82 inches. The ancient Greek foot, = 

 12.09 inches. — Orig. 



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