LECTURES. 57 



dense because it has been warmed by contact with the Earth, so we 

 find storms exists in the Sun's atmosphere, but of far greater magni- 

 tude. Flames are shot out from the burning envelope round the 

 Sun travelling at the rate of more than 30 miles a second and reaching 

 more than 10,000 miles, while their smoke may extend for 70,000 miles. 

 These are best seen during an eclipse when the bright disc of the Sun 

 is shut off from us by the Moon. 



The Moon has always been an object of deep interest to man. It 

 is our closest heavenly companion. If you went in a train to the 

 Moon and travelled at the rate of 60 miles an hour you would get there 

 in 8 months, while you would take 260 years to get to the Sun. The 

 Moon always shows the same face to us and therefore is rotating 

 round its axis once every time it moves round the Earth. It has 

 no atmosphere. This we know because when the Moon passes 

 between us and a star, the star disappears suddenly and does not first 

 become blurred as it would if the Moon's atmosphere came between 

 us and the star before the Moon itself intervened. 



The Moon of course attracts the Earth and all things on it : when 

 that thing happens to be water the water is piled beneath the Moon 

 and so tides are produced. The Sun too has a similar action but the 

 Moon tides are so much greater than the Sun tides that for our 

 present purpose we may neglect the latter. Owing to the huge body 

 of water being pulled round by the Moon a certain amount of friction 

 is set up which tends to check the motion of the Earth, and this 

 action of the Moon on the Earth is accompanied by an action of the 

 Earth on the Moon, and as our speed of rotation gets slower the 

 Moon gets further off. Follow this line of reasoning backwards 

 instead of pursuing it forwards and it is easy to see that long, long ago 

 the two bodies were close together and in very rapid movement the 

 Moon rushing round the Earth and very close to it, the Earth at the 

 same time spinning round on its own axis at a very rapid rate. 



Before that it seems probable that they were together as a mass 

 of nebulous matter, such as we can see in Andromeda or Orion now 

 a mass of glowing gas which as it cooled shrunk till it condensed to a 

 more or less spherical ball. Along some line of weakness a rupture 

 occurred and a part of our mass got ejected into space and became 

 our satellite, the Moon. The subsequent difference in the histories 

 of the two bodies is simply due to their difference in size. 



The Earth as it cooled formed a solid crust, which got repeatedly 

 broken up by the internal attraction, but it was formed again and 

 again, until its thickness was such that it remained permanent, after- 



