The Science ot the Weather 787 



of the atmosphere, and the many beautiful spectacles seen at 

 sunrise and sunset are also due to the diffraction and scattering of 

 the light-rays from the sun. The dust particles and water droplets 

 in the atmosphere have the power of scattering first the blue-violet 

 and then the green components of white light, and so causing the 

 light to change through yellow into red. The glorious tints of 

 the rainbow are due to the reflection and refraction of the rays 

 of light from the sun by the drops of rain, which act like tiny 

 prisms and break up the white light into the rays of varied colours 

 of which sunlight is really composed. But no appearance in our 

 skies can vie in mystery and delicate beauty with the aurora, whose 

 shimmering rays of yellow-green, rose, or crimson light at times 

 transfigure the starlit skies of winter. The aurora occurs some 

 fifty miles up in our atmosphere, and is generally regarded as 

 being due to electrical rays of the nature of the cathode rays 

 which are given out by the sun in greatest quantity at the times 

 of sun-spot maxima. The frequency of auroras, of sun-spots, and 

 of magnetic storms within the earth show a sympathetic connec- 

 tion with each other, and are in all probability due to the same 

 original cause. Contrary to general belief, the aurora does not 

 presage stormy weather. 



10 



Periodic Variations 



The question is often asked whether our weather is changing 

 for the worse, and to this the answer is in the negative. Very 

 slight variations in temperature and in raininess are known to 

 recur in some places and to have some agreement with the sun- 

 spot cycle of about eleven years, and there have been alternations 

 from dry and warm periods to cool and wet ones, but the periods 

 are very irregular and the changes slight. 



The factor that does really make a difference to our weather 

 in Britain is the average position of the cyclone-track during the 



