Show I 1 DAYS FOUR HOURS LONG NG th was somme some time AO ago and ad th the earth traveled Tra much aluch raster today to day is longer than yeste yesterday iday toi morrow morro vr will be longer than today to day the difference is so small that even in the course of ages it can hardly be said to have been distinctly established by observation says the story of the heavens we NV do not pretend to t say how many centuries have elapsed since the day was even one second shorter than it is at present but centuries cen furies are arc lot the units which we may employ in bidal tidal evo evolution lutio n A million years ago it jis L quite qu ita probable that the divergence of the length of the day from the present v arit inave t roay may h have been very considerable lt let L t us take a glance back into the t lie pro found depths vl of time past and atiel s sec ac what the tides aidt s haye to tell us li 11 the present order of taisy has ha s lasted the day must have becu fc hurter and shorter the farther we look back into the dim past the day is now four was once six hours how much farther ean can we go fo once the six hours is p past ast we begin td tcP approach a limit which must at ome tome t point bound our prospect the shorter the day the more is the earth bulged at the equator the more the earth is bulged at the equator the greater is esthe the strain put upon the materials of the earth by the centrifugal g a force sit of I 1 its rotation it if the ea earth r th were w ere to th go too fast it would be unable fo cohere to together gither it would separate into I 1 n to pieces just as a grindstone driven too rapidly is rent asunder with violence here therefore we discern in the remote past a barrier which stops the present argument there is a certain critical velocity which is the greatest that the earth could bear without nak of rupture but the exact exa ct amount of that velocity is a question not very easy to answer it depends upon the nature of the materials of the earth it depends upon the temperature it ihde depends upon the effect of pressure and on CM other details not accurately known to us an estimate of the critical velocity loo city has however been made and it hsi has been shown that the shortest period of rotation which the earth could have without flying into pieces is is about three or four hours hourd the doctrine I 1 of tidal evolution has thus conducted us to the conclusion that at some so me incon inconceivably ceiva bly remote epoch the earth was spinning round its axis in a period approximating to three or six hours |