18 



On "The British Standards." 

 By Me. E. B. Lucas. 

 [Bead December 1, 1885.] 

 Plates VIL-XI1I. 



I need not lay any stress upon the importance of absolute 

 accuracy o£ measurement, and especially of standards being 

 accurate, and though to those unconnected with scientific 

 matters such errors as are observed and corrected in verifying 

 standards would seem unimportant, yet scientifically the 

 dimensions treated of will be quite appreciable. 



It has been found that " no two primary standards, even, 

 have ever been compared between which some difference has 

 not been found," and this being the case it becomes a question 

 as to the limit of error, or put in another form, the amount of 

 trouble to which it is advisable to go in order to obtain the 

 highest amount of accuracy. 



The British Board of Trade has settled that the limit of 

 error to be allowed in the standard yard line measures is not to 

 exceed '003 of an inch, or x a * of the yard which corresponds 

 to a range of temperature of 10° Fahr. The actual expansion 

 of the metal of which primary standards are usually made is 

 '000341 inch for each degree of Eahr. This metal is a mixture 

 of copper, sixteen ounces ; tin, two and a half ounces ; zinc, 

 one ounce ; and is called " Baily's metal." 



To observe with sufficient closeness to note such dimensions, 

 a comparing apparatus, fitted with microscopes, has been 

 designed by Mr. Sheepshanks, a well-known authority in such 

 matters, and is now in use at the Board of Trade offices at 

 Westminster, where all the standards are kept. 



"When in London lately I met with the most courteous 

 reception by Mr. Chaney, the warden of the standards, who 

 has expressed and shown a willingness to distribute infor- 

 mation on these matters that is highly praiseworthy. When 

 it is possible to obtain valuable information from so high an 

 authority given so generously it is unwise not to seek it. I 

 accordingly made use of the opportunity, and am now in the 

 possession of a mass of valuable information on the subject. 



It was not until the year 1867 that the British Government 

 saw the importance of establishing upon a firm and reliable 

 basis a set of standards, devoting to the purpose a special 



