Fog signals are also used on railways during foggy weather; they consist of cases filled with detonating powder, which are laid on the rails and exploded by the engine when it runs over them. The Story in a Watch[5] Clocks and watches are often called “timekeepers,” but they do not keep time. Nothing can keep it. It is constantly flying along, and carrying us with it, and we cannot stop it. What we call “time keepers” are really time measures, and are made to tell us how rapidly time moves, so that we may regulate our movements and occupations to conform to its flight. Of course, you understand that measurement of anything is the comparing of it with some established standard. So that if you want to measure the length of anything you use a rule or a yard stick, or some other scale which is graduated into fractions of the whole standard measure. Do you know that the United States government has in a secure, fireproof vault, in one of the government buildings in Washington, a metal bar which is the authorized standard “yard” of this nation? It is a very carefully made copy of the standard yard of Great Britain. I believe that each one of the United States has also a standard which must agree in length with the government, or national standard. The same thing is true concerning standards of capacity, and standards of weight. But no vault can contain the authorized standard of time. Yet there is such a standard. And it is as accessible to one country as to another, and it is a standard which does not change. But, because all other time measures are more or less imperfect, our government tries to compare its standard clock with the ultimate standard every day.