4 o2 THE POPULAR SCIENCE MONTHLY. 



court of Rome saw how unwisely she had acted in deciding a question 

 beyond her competence, thus laying herself open to the danger of 

 being the next day convicted of error, it became her interest, no less 

 than the interest of Science, to distinguish clearly between the two 

 domains, Science and Faith. If, nowadays, she avoids entering into 

 scientific controversies, it is because she has been taught by experience 

 that a decision might compromise her. Her authority could hardly 

 stand after a second edition of the sentence in which she once forbade 

 the sun to stand still and the earth to revolve. 



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DISTANCE AND DIMENSIONS OF THE SUN. 



By Professor C. A. YOUNG, 



OF DARTMOUTH COLLEGE. 



THE problem of finding the distance of the sun is one of the most 

 important and difficult presented by astronomy. Its importance 

 lies in this, that this distance the radius of the earth's orbit is 

 the base-line by means of which we measure every other celestial dis- 

 tance, excepting only that of the moon ; so that error in this base 

 propagates itself in all directions through all space, affecting with a 

 corresponding proportion of falsehood every measured line the dis- 

 tance of every star, the radius of every orbit, the diameter of every 

 planet. 



Our estimates of the masses of the heavenly bodies also depend 

 upon a knowledge of the sun's distance from the earth. The quan- 

 tity of matter in a star or planet is determined by calculations whose 

 fundamental data include the distance between the investigated body 

 and some other body whose motion is controlled or modified by it ; 

 and this distance generally enters into the computation by its cube, 

 so that any error in it involves a more than threefold error in the re- 

 sulting mass. An uncertainty of one per cent, in the sun's distance 

 implies an uncertainty of more than three per cent, in every celestial 

 mass and every cosmical force. 



Error in this fundamental element propagates itself in time also, 

 as well as in space and mass. That is to say, our calculations of the 

 mutual effects of the planets upon each other's motions depend upon 

 an accurate knowledge of their masses and distances. By these cal- 

 culations, were our data perfect, we could predict for all futurity, or 

 reproduce for any given epoch of the past, the configurations of the 

 planets and the conditions of their orbits, and many interesting prob- 

 lems in geology and natural history seem to require for their solution 

 just such determinations of the form and position of the earth's orbit 

 in by-gone ages. 



