OF A.ETS AND SCIENCES. 277 



the degree at which each bar is standard is given. These bar have 

 all been distributed among different governments. 



The standards prepared by Mr. Sheepshanks were legalized by act 

 of Parliament passed July 30, 1855. 



Two platinum bars — one a line-measure and the other an end- 

 measure — form the basis of the metric standard of length at present 

 in use in Great Britain. These bars have the following dimensions : — ■ 



Line-Meter. End-Meter. 



Length, 41.0 inches. 39.37 inches. 



Breadth, 1.0 1.00 



Thickness, 0.211 0.287 



The line-meter has the words " Royal Society, 45," engraved on the 

 under side. The defining lines run nearly across the face of the bar, 

 and there is no cross line to indicate the exact points from which 

 measures are to be made. Arrows, arbitrarily placed, now indicate 

 the points from which all the later measures have been made. The 

 lines on this bar have become so obliterated that it is found impossible 

 to see them with the method of illumination formerly in use. At the 

 request of Mr. Chaney, I employed Mr. Crouch, of London, to con- 

 struct two new objectives for the microscopes of the comparator, to 

 which were adapted two of Tolles's interior illuminators for viewing 

 opaque objects. The magnifying power was increased between five 

 and six times, and the illumination was so much improved that there 

 was no difficulty whatever in seeing the lines of this bar. 



The end-meter has the words "Metre a Bouts" engraved on one 

 side, and the words " Fortin a Paris, Royal Society 44," on the other 

 side. At the present time, this standard is not in a condition to admit 

 of accurate measurements. The edges of the end surfaces are in- 

 dented, and there is a raised burr on one end. These bars, together 

 with the original bars compared by ilassler in 1N32, are the only 

 recognized standards which have ever been compared with the Meter 

 of the Archives. They form, therefore, the real basis of our present 

 knowledge of the relative length of the meter and of the yard. 1 shall 

 presentty recur to this important matter. 



The line-meter was transferred by Troughton and Simms to a bar 

 of Baily's metal in 1869. Kater's reduction to the Meter of the 

 Archives was applied in the transfer. The Imperial Yard was also 

 transferred to tin- same bar. The lines are drawn upon gold plugs, 

 which are not, however, inserted in wells. At the distance of 39.37 

 inches from the first plug the '"meter plug" is inserted. This meter is 



