H. LENGTH. 43 



228. Standard Five-Inch Scale, in smoky agate, for micro- 

 scope sight. Prof. Piazzi Smyth. 



The material, which came from Brazil, and was worked up and divided 

 to order by M. Jules Salleron, Paris, was chosen as being a natural product 

 of almost infinite age, and therefore settled condition, harder than steel and 

 utterly unoxidisable. The particular standard length adopted is shown for 

 microscopic sight. It depends not on one pair only, but on 20 available pairs 

 of lines, each five inches apart, drawn with a fine diamond point, and is in- 

 tended to typify both one fifth of the sacred cubit of Israel and one 50 

 millionth of the earth's semi-axis of rotation. 



229. Standard Five-Inch Scale, in white chalcedony, for 

 microscope sight. Prof. Piazzi Smyth. 



This material, which came out of some ancient Roman palace, is chosen 

 for the same reasons as that last described. The scale is divided on the same 

 system. 



230. Standard Five-Inch Scale, in red porphyry, for 

 microscope sight. Prof. Piazzi Smyth. 



This material came from an Imperial Roman palace to which it had been 

 taken under the Csesars from some far more ancient Egyptian temple. It was 

 originally quarried by the Egyptians of 3,500 years ago in the rich porphyry 

 district between Thebes and the Red Sea, and it has been adopted for the same 

 reasons as the preceding examples, and the scale is divided on the same 

 system. 



232. Standard of Length, derived from the earth's polar 

 axis, which is unique and common to all terrestrial meridians. 



Professor Hennessy. 



This standard is a bronze bar, which, at 1 5 of temperature centigrade, is 

 equal to the fifty millionth part of the earth's axis. This standard was first 

 proposed by Professor Hennessy, and a similar standard was afterwards sug- 

 gested by Sir John Herschel. 



233. Steel Chain, of fifty links, whose total length is the 

 millionth part of the earth's axis, or very nearly 500*5 English 

 inches. It is nearly equal to the half chain of two perches in Irish 

 plantation measure. Professor Hennessy. 



235. Standard Yard Measure, German Silver, with one 

 chamfer divided to inches and lOths. Temperature 60 Fahrenheit. 



Elliott Brothers. 



239. Steel Tape Measure, 66 ft. For testing tapes, divided 

 to feet and inches on one side and links on the other. 



Elliott Brothers. 



244. Scales, of boxwood, showing the equivalents of English 

 and Foreign measures of length. Aston fy Mander. 



