52 LIGHT SCIENCE FOR LEISURE HOURS. 



solar eclipses, there are other discoveries due also to 

 the observation of total eclipses, though in very ancient 

 times, which are as full of interest. It sounds in- 

 credible, but is nevertheless strictly true, that, owing 

 to comparatively rough observations of ancient eclipses, 

 modern astronomers have learned that the moon is 

 gradually drawing nearer to the earth ; and further, 

 that the rate of the earth's rotation on her axis is 

 slowly but surely diminishing, insomuch that at some 

 far distant epoch the day will last as long as a lunar 

 month. Nor do the facts that the approach of the 

 moon will in time be changed into recession, and that 

 the lengthening of the day takes place so slowly that 

 millions of centuries must elapse before it is completed, 

 diminish the interest which attaches to these tokens 

 of mutability in relations which had once been regarded 

 as altogether unchangeable. 



But let us turn to those discoveries which belong 

 more especially to the now wide department of science 

 called solar physics. 



It does not appear that the ancients had any idea 

 that observations made during total eclipses could 

 afford any information as to the condition of the great 

 central luminary of our system. To them the chief 

 interest of solar and lunar eclipses consisted in the 

 evidence they afforded of the exactness of astronomical 

 computations, and the soundness of the general prin- 

 ciples on which those computations were based. Nor 

 do we find that any of the observed phenomena of total 

 eclipses attracted the special attention of ancient 



