306 PHILOSOPHICAL TRANSACTIONS. [ANNO 17 Q8. 



believe had never seen the light for 35 years before. It is a brass rod or bar, about 

 39 inches long, and 1 inch square, inclosed in a mahogany frame, inscribed 



" Standard *%£ J 758;** at each extremity of it is a gold pin, of about ^ inch in 



Geo. 3d 



diameter, with a central point, and these points are distant = 36 inches. It bears 

 however no divisions; but there was found with it, in another box, a scale divided 

 into 3d inches, with brass cocks at the extremities, for the purpose of sizing or 

 gaging other scales or rules by. Besides these, I found another standard, in size, 

 and in all respects, similar to the last, inscribed 1 760, having been made for an- 

 other committee, that sat in that year; this also was accompanied with a similar 

 divided scale of 36 inches. These bars being too thick to be conveniently placed 

 under the microscopes of my instrument, the interval of 36 standard inches was 

 laid down on my scale with a beam-compass, 2 fine points made, and, compared 

 with Troughton's divisions, was = 36.00023 inches; the thermometer being at 

 64°. I then examined the other standard, marked t( Standard, 1760," and found 

 it to agree exactly with that of 1758; at least it did not differ from it more than 

 .0002 inch. 



I was now to examine the old standards kept in the Exchequer: these, Mr. 

 Charles Ellis, Deputy Chamberlain of the Tally Court at the receipt of the Exche- 

 quer, was so good as to supply me with ; viz. the standard yard of the 30th of Eliz. 

 1588, and also the standard ell of the same date. These are what have been con- 

 stantly used, and are indeed the only ones now in use, for sizing measures of 

 length.* They are made of brass, about 0.6* inch square, and are very rudely 

 divided indeed, into halves, quarters, 8ths, and l6ths; the lines being 2 or 3 

 hundredths of an inch broad, and not all of them drawn square, or at right angles 

 to the sides of the bar, so that no accuracy could possibly be expected from such 

 measures. However, the middle point of these transverse lines, between the sides 

 of the bar, was taken as the intended original division ; and these divisions, such 

 as they were, were transferred, by a dividing knife, to the reverse side of my brass 

 scale made by Mr. Troughton, the thermometer being at 63°; and, at my leisure 

 afterwards, I found as follows. The ends of these venerable standards having been 

 bruised a little, or rounded, in the course of so many years' usage, I conceived a 

 tangent to be drawn to the most prominent part, which was about the centre or 

 axis of the bar, and this point being referred to Troughton's scale, between 6 and 

 42 inches, the entire yard of 1588, measuring from one extremity to the other, 

 was found to be shorter than this, by — .007 inch : but these comparisons will be 

 better exhibited in a table, as follows. 



* There was also a standard yard of Henry vn., but of very rude workmanship indeed; now quite 

 laid by, and at what time last used, no information remains ; but of this more hereafter. — Orig. 



