 In the 1860s, inspections of the prototype metre revealed wear and tear at the measuring faces of the bar and also that the bar was wont to flex slightly when in use.In view of the doubts being cast on the reproducibility of the metre and the kilogram and the threat that a rival standard might be set up, Napoleon III invited scientists from all the world's nations to attend a conference in Paris.In July 1870, two weeks before the conference was due to start, the Franco-Prussian War broke out.