158 ON SOME RECENT SUN SPOTS. 



The Sun Spots proper are unquestionably cavities or depres- 

 sions in the photosphere, filled with gases or metallic vapours, 

 and probably cooler than the surrounding portions. The fact 

 that they are cavities is distinctly shown by the appearance of a 

 spot when seen in perspective near the edge of the solar surface. 

 The foreshortening of the spot is very manifest. A spot of any 

 dimensions is always surrounded by an extension of a lighter 

 shade called the penumbra, the centre or darker portion being 

 called the umbra. This is plainly shown in the illustrative 

 sketches and photos. The dimensions of these spots vary 

 enormously, from a mere point only just detectable in a powerful 

 telescope to a capacity adequate to take in all the planets of the 

 solar system, not excepting Jupiter, the largest itself almost a 

 semi-sun. Dr. Young estimates that the diameter of the umbra 

 ranges from 500 to 1,000 miles in the case of a very small one, 

 and from 50,000 to 60,000 miles in the case of a larger one. The 

 penumbra surrounding a group of spots is sometimes 150,000 

 miles across. Those seen by the naked eye are often much 

 larger. The depth of the umbra is very difficult to determine, 

 but seldom exceeds 3,000 miles. 



The larger Sun Spots of last autumn now claim our brief 

 attention. They were chiefly seen in October and November, 

 but the clouded condition of the skies during those months 

 prevented adequate observation. Though drawings and photos 

 were secured, they were not so satisfactory as desired. 



One word about the connection between Sun Spots and 

 terrestrial weather. After a careful consideration of the evidence 

 to hand pro and con., we conclude that such direct connection 

 fails to be established, and they have little, if any, influence on 

 our rainfall or weather. We confess, however, that the problem 

 has not been fully thrashed out. That there is a connection 

 between Sun Spots and terrestrial magnetism is, we venture to 

 think, fairly, if not fully, established, as the recorded curves of 

 each very closely coincide. This is shown by the registers of 

 each as kept by the Royal Observatory and other associated 

 authorities. So, as far as magnetism affects our atmosphere in 



