XII. 



ON THE 



COMPENSATION MEASURING APPARATUS 



OF THE 



GREAT TRIGONOMETRICAL SURVEY OF INDIA. 



By captain EVEREST, 



Berujal Artillery, 



F.R.S. M.A.S. r.G.S. S.C. SURVEYOIt GENERAL, AND STIPEHTNTENDENT OF THE 

 GREAT TIUGONOMKIKICAL SURVEY OF INDIA. 



[Being the substa>ice of a Lecture delivered in Vlustration of the Meaturing Apparatus, before the Physical Class, 



on the nth March, 1831.] 



Nothing seems easier, at first sight, than to measure a straight h'ne. If, 

 for example, it were wanted to ascertain the length of the room we are in, 

 or the table at M'liich we are seated, the mode commonly used on such 

 occasions would be to lake a loot ride and try how many feet and inches 

 it was, and this would be (|iiiic a sufficient solution, provided that there 

 was no further object in view. But suppose it were necessary, for any 

 particular purpose, to know the cxiu l relative lengths o(" two rods or bars, 

 one of which had been dctcriuiiuMl iu the national un asuro ol' I'ranco, and 

 the other in that ol"(irc'al Hntaiii IIcmo, at liisl siuhi, is a v(M-y tlillVrc-nt 

 State of the case, for tlio l'jiuli--li rod has boon uuMsur(Hl w ith a loot rule, 

 and so has the Im-cucIi ; l)ul ihuugli iIicn blioiilil bo of portocily oc^ual size, 

 the lengths would not be expressed by the sjanic number. 



3 .\ 



