46 LIGHT SCIENCE FOR LEISURE HOURS. 



fore appreciable, scale by a powerful telescope, should 

 speak of the connection between this movement arid 

 the intrinsic worth of a sovereign ? The natural 

 thought with most men would be that " too much 

 learning " had made the astronomer mad. Yet, when 

 we come to inquire closely into the question of a sov- 

 ereign's intrinsic value, we find ourselves led to the 

 diurnal motion of the stars, and that by 110 very intri- 

 cate path. For, What is a sovereign ? A coin contain- 

 ing so many grains of gold mixed with so many grains 

 of alloy. A grain, we know, is the weight of such and 

 such a volume of a certain standard substance that is, 

 so many cubic inches, or parts of a cubic inch, of that 

 substance. But what is an inch ? It is determined, 

 we find, as a certain fraction of the length of a pendu- 

 lum vibrating seconds in the latitude of London. A 

 second, we know, is a certain portion of a mean solar 

 day, and is practically determined by a reference to 

 what is called a sidereal day the interval, namely, be- 

 tween the successive passages by the same star of the 

 celestial meridian of any fixed place. lliis interval is 

 assumed to be constant, and it has indeed been de- 

 scribed as the "one constant element'" known to as- 

 tronomers. 



"We find, then, that there is a connection, and a 

 very important connection, between the motion of the 

 stars and our measures, not merely of value, but of 

 weight, length, volume, and time. In fact, our whole 



