120 ANSWERS TO PRACTICAL QUESTIONS 



length of time. (Read Proctor's " When the Sea was Young," 

 in Poetry of Science.) 



57 Show how, if the Nebular Hypothesis be accepted, 

 the fashioning of a planet must require an enormous 



length of time. 



(See Astronomy, p. 255.) 



The experiments of Bischof upon basalt show that the earth 

 would require 350 millions of years to cool down from 2,000 

 C to 200 0. This enormous period would represent only one 

 stage in the process of the earth's development. (Read Win- 

 chell's World Life.) 



58. Do we know the cause of gravitation ? 



(See Astronomy, note, p. 23.) 



283 1. In what constellation is Job's Coffin? The 

 Letter Y? The Scalene Triangle? The Dipper? The 

 Kids ? The Triangles ? 



Job's Coffin is in Delphinus ; the Letter Y, in Aquarius ; 

 the Scalene Triangle, in Aries ; the Big Dipper, in Ursa Major ; 

 the Kids, in Auriga; and the Triangles, between Almach and 

 Arietis. 



2. Name some facts in the solar system for ivhich the 

 Nebular Hypothesis fails to account. 



It is very difficult to explain, on the basis of the Nebular 

 Hypothesis, why the axes of certain of the planets are so 

 greatly inclined, and, especially, why the velocity of the rota- 

 tion of the inner moon of Mars should so far exceed that of 

 Mars itself. 



3. Which is probably hotter, a yellow or a red star ? 



(See Astronomy, note, p. 241.) 



When we heat a piece of iron, it first becomes red-hot, 

 then, as the temperature rises, other colors appear, until, 

 finally, it becomes dazzling white. (See Physics, p. 183.) 



4. Are any of the stars likely to collide with each other ? 



Nothing strikes the astronomer more forcibly than the 

 thought of the desolateness of space. A vast gulf, more than 



