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C,C. NATURAL HISTORY SOCIETY. 



LECTURES. 



"THE ROMANCE OF ASTRONOMY." 

 By a. a. Bourne, Esq. 



]F a stone be attached to a string and then swung 

 round there is a certain force keeping the stone 

 in the circle it describes. In the case of the 

 planets which are describing curves which are 

 nearly circles, this force is the force of attraction 

 to the Sun, and since to every force there is an 

 equal and opposite reaction there is also a force, 

 called the centrifrugal force tending to force the 

 planets away from the Sun. Without this centrifrugal force the planets 

 would be absorbed into the Sun. 



The heat given out by the Sun is enormous, one square foot being 

 able to supply 7,000 Horse Power ! and with this tremendous loss of 

 heat it is natural to look ahead and picture to ourselves the Sun 

 a comparatively cold body. If the Sun were a solid body we might 

 expect a few centuries to make an appreciable difference in its 

 temperature, and the only reasonable explanation we can give of its 

 keeping up its temperature is that it is a huge mass of glowing gas, at 

 any rate in its outward parts. As it parts with its heat it shrinks and 

 so the heat remaining is sufficient to keep up its temperature. The 

 total heat is less, but the body it is heating is smaller and so the 

 temperature is as high as before. 



If we could only measure the rate of decrease of the Sun's size 

 we could satisfy ourselves on this point, but the Sun might decrease 

 its diameter by 86 miles and yet our telescopes would not be able to 

 inform us of the fact. Still though it may shrink and keep its 

 temperature up for a time, its ultimate fate is to grow cold. 



Just as we have storms in our atmosphere owing to colder and 

 therefore denser air settling down and replacing air which is less 



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