64 IN STARRY REALMS. 



not be a doubt that to some extent the earth is affected by 

 the unremitting action of the tides ; the consequence is 

 that the rapidity with which the earth rotates upon its 

 axis is gradually declining. 



One result of this can be stated in a very simple 

 manner. The length of the day must be increasing. 

 It is true that this gradual stretching of the dav 

 is very slow ; it is indeed quite inappreciable in so far 

 as our ordinary use of the day as a measure of time is 

 concerned. The alteration almost eludes any means of 

 measurement at our disposal. Even in a thousand years 

 the change is so small that the diminution in the length of 

 the day is only a fraction of a second. We can doubtless 

 afford to disregard so trifling a variation in our standard 

 of time so far as the period contemplated in mere human 

 affairs is concerned. In fact the change is absolutely devoid 

 of significance within such periods as are contemplated 

 since the erection of the Pyramids, or indeed since any other 

 human monument has been reared. We must not, how- 

 ever, conclude that the change in the length of the day has 

 no significance in earth history. Of late years it has be- 

 come known that this alteration in the day is connected 

 with an important chapter in the remote history of 

 this globe. In fact there is hardly a more interesting 

 doctrine in modern science than that which deals with this 

 subject. I have explained the phenomena somewhat fully 

 in my little volume entitled " Time and Tide," in which I 

 have endeavoured to sketch the remarkable evolution 

 through which the earth seems to have passed. I must, 

 however, here give a few of the leading features in the 

 story, for it would be quite impossible to exclude it altq- 



