100 SIB WM. AND CAROLINE HEESCHEL, 



would Herschel have said to the wonderful photo- 

 graphic representations of these spots given by 

 Professor Langley, in his New Astronomy ; spots 

 which are one billion square miles in size; more 

 than five times the surface of the land and water 

 on the earth ? He saw, as astronomers to-day see, 

 that heat cannot be produced without expenditure 

 of force ; and that the sun is probably cooling, even 

 though scarcely perceptibly for ages to come. He 

 saw what science now generally concedes, the rise 

 and fall of the solar system ; its gradual fitness for 

 the coming of man, through almost coiintless cen- 

 turies ; and its final unfitness, when his generations 

 shall have gone forever. 



He wrote much about the Milky Way, believing 

 at first that it could be completely resolved into 

 stars, about eighteen millions of them ; but later 

 he changed his theory, having found so much 

 nebulous matter in a state of condensation as 

 though new worlds were forming, possibly to be 

 the homes of some new race, or of man in the 

 ages to come. 



His study of the variable stars attracted wide 

 attention. He found that the star Mira Ceti was 

 for several months invisible to the naked eye ; 

 then it grew brighter and brighter, and finally 

 disappeared for months, as before. He saw that 

 other stars are periodic, and came to the con- 

 clusion that this is occasioned by the rotation of 

 the star upon its axis, by which different parts of 

 its surface are presented to us periodically. 



