OUR CHIEF TIMEPIECE LOSING TIME. 61 



open ocean may not be strikingly indicative of " work 

 done ; " but when we see the behavior of the tidal 

 wave in narrow channels, when we see heavily-laden 

 ships swept steadily up our tidal rivers, we cannot but 

 recognize the expenditure of force. Now, where does 

 this force come from ? Motion being the great " force- 

 measurer," what motion suffers that the tides may 

 -work ? AVe may securely reply, that the only motion 

 which can supply the requisite force is the earth's 

 motion of rotation. Therefore, it is no idle dream, 

 but a matter of absolute certainty, that, though slowly, 

 still very surely, our terrestrial globe is losing its rota- 

 tion-movement. 



Considered as a timepiece, what are the earth's 

 errors? Suppose, for a moment, that the earth was 

 tinned and rated two thousand years ago, how much 

 has she lost, and what is her " rate error ? " She has 

 lost in that interval nearly one hour and a quarter, and 

 she is losing now at the rate of one second in twelve 

 weeks. In other words, the length of a day is now 

 more by about one-eighty-fourth part of a second than 

 it was two thousand years ago. At this rate of change, 

 our day would merge into a lunar month in the course 

 of thirty-six thousand millions of years. But after a 

 while, the change will take place more slowly, and 

 some trillion or so of years will elapse before the full 

 change is effected. 



Distant, however, as is the epoch at which the 



