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XXXV. 



TABLES FOE THE EASY CONVERSION OF BRITISH INTO 

 METRICAL MEASURES. By G. JOHNSTONE STONE Y 

 D.Sc, F.R.S. 



[Read March 20, 1889. J 



Two comparisons between the metre and the yard have been made 

 with ' great care,' viz. : Captain Kater's (which is that commonly 

 quoted) and Captain Clarke's (see Phil. Transactions, 1867). 



According to Kater, the metre = 39*37079 inches. 



According to Clarke, it = 39*37043 „ 



Whence 



Kater's yard = 914*38348 mm. 



Clarke's „ = 914-39180 „ 



These determinations differ from one another by nine parts in 

 a million, or by nearly one part in 100,000. Hence an error of 

 one part in 100,000 in such comparisons cannot be with certainty 

 detected even with the help of the appliances used by these 

 observers, and with the extreme care taken by them. This one 

 part in 100,000 is about half the amount by which standards of 

 length (of brass or gunmetal) expand for 1° C. of temperature. 



Of the two determinations Captain Clarke's is the more recent, 

 and is also entitled to most confidence. Adopting it — 



The metre = 39*370432 inches, 



= 39*37 (1 + -000,011), 

 and the yard = 914*39180 millimetres, 



= 914*4 (1 - -000,009). 



Hence the error of taking 39*37 inches as the length of the 

 metre, and 914*4 mm. as the length of the yard, amounts in the 

 first case to but little more than one part in 100,000, and in the 

 second case to somewhat less than that amount. 



These are errors which may be legitimately neglected in all 



