The copper coins, changed to bronze in about 1854, are pieces of 10 and 5 centimes, the latter equivalent to the old sou, so that the franc is commonly called a 20-sou piece, and the other silver coins, nominally of 5, 2, and 1/2 franc, are called in the same way _pièces de cent sous_, _quarante sous_ and _dix sous_. The centime is so rarely seen as to be practically non-existent, and the decimal system not allowing the half or quarter of the 5-centime piece or sou, great inconvenience is felt by the poor,[53] yet the symmetry of the system has been marred by the issue of nickel quarter-francs, of a size which makes them often undistinguishable from francs. But this is 25 centimes, while the half-sou would be written 2·5 centimes, marring the symmetry of the centime column in accounts—where practically it would never appear. Footnote 53: Thus if bread is 25 centimes or 5 sous the kilo, a single pound or half-kilo of bread cannot be bought at this price. Since the adoption of a gold standard under the second Empire, the gold 20-franc piece is the standard of exchange, and of payments in trade. It weighs 6·451 grammes = 99·5635 grains; it is of 0·900 fineness (= 22-1/5 carats) and thus contains 86·6071 grains of pure gold. Its exchange value is usually 15_s._ 10-1/2_d._, our sovereign being equal to 25 francs 20 centimes. The system of international currency has led to the French currency containing coins, both gold and silver, of strange devices, and the necessity of placards in shops showing figures of the numerous coins which should not be accepted. Considerable vigilance is necessary to avoid taking coins not current, or taking for francs the nickel five-sou pieces scarcely distinguishable from them except in a good light. _Temperature_ The French thermometer, called Centigrade (the proper term would have been centesimal), is on Celsius’s scale, of 100 degrees between the freezing and boiling points of water, under the normal atmospheric pressure, which for France is 760 millimetres = 29·92 inches. _Metric Measures of Time_ These are dropped, officially, at present; but they may be re-established, for they were the essential part of the Republican system. Ardent republicans constantly claim their re-establishment, and sound republican newspapers, dated according to the republican calendar, take care that this shall not be forgotten. Scientific journals demand the re-establishment of decimal time and decimal degrees; for even to sell eggs or handkerchiefs by the dozen is a sin, and ought to be made a crime, against the decimal system.