42 LIGHT SCIENCE FOR LEISURE HOURS. 



not been in vain. In fact, we are able to announce, 

 with an approach to positiveness, that our great terres- 

 trial time-piece is actually losing time. 



In our moon we have a neighbour which has long 

 been in the habit of answering truthfully questions 

 addressed to her by astronomers. Of old, she told 

 Newton about gravitation, and when he doubted, and 

 urged contradictory evidence offered as men in his 

 time supposed by the earth, she set him on the 

 right track, so that when in due time the evidence 

 offered by the earth was corrected, Newton was pre- 

 pared at once to accept and propound the noble theory 

 which rendered his name illustrious. Again, men 

 wished to learn the true shape of the earth, and went 

 hither and thither measuring its globe ; but the moon, 

 meanwhile, told the astronomer who remained at 

 home a truer tale. They sought to learn the earth's 

 distance from the sun, and from this and that point 

 they turned their telescopes on Venus in transit ; but 

 the moon has set them nearer the truth, and that not 

 by a few miles, but by 3,000,000 or more. We shall 

 see that she has had something to say about our great 

 terrestrial time-piece. 



One of the great charms of the science of astro- 

 nomy is, that it enables men to predict. At such and 

 such an hour, the astronomer is able to say, a celestial 

 body will occupy such and such a point on the celes- 

 tial sphere. You direct a telescope towards the point 

 named, and lo ! at the given instant the promised orb 

 sweeps across the field of view. Each year there 



