Show arlic or one of the difficult problems in practical la to make a straight edge how difficult it is may be judged from an incident which occurred in the of J A the astronomical instrument maker A customer asked mr bat ix tin arct of a perfect straight etl of glass sa inches long it can t be made absolutely I 1 er feet said mr nr ashear but it coald be luark with a limit of error amounting to only a fraction of a wae length of light how much would that cost about y it turned out that the customer wanted the bilge for n scraper and that an arror of one sixty fourth of an inch bould bare teen for bis pui pose youth a |