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Review of Science and Industry, 



A MONTHLY RECORD OF PROGRESS IN 



SCIENCE, MECHANIC ARTS AND LITERATURE. 



VOL VI. NOVEMBER, 1882. NO. 7. 



ASTRONOMY. 



THE COMING TRANSIT OF VENUS. 



PROf. H. S. S. SMITH, UNIVERSITY OF KANSAS. 



The distance between the Earth and Sun is the astronomer's foot rule. With 

 it he measures distances in the solar system and even reaches out and spans the 

 almost endless spaces between the stars. It is, then, of prime importance to him 

 that he know the exact measure of this, his measuring rod. 



Ever since the time when Kepler proved and refined the Copernican theory, 

 this problem has been one of the most important and, at the same time, one of 

 the most difficult with which astronomy has had to deal. It has called into exer- 

 cise the highest powers of mathematical genius, has demanded and obtained, de- 

 cided improvements in astronomical instruments and rnethods of observation, and 

 has received more pecuniary aid than any other purely scientific problem. 



There are several methods available for the determination of this measure. 

 Among them may be mentioned that by the parallax of Mars and of the minor 

 planets, that by the velocity of light, that by inequalities in the motion of the 

 Moon, and that by the variation of the attraction of the earth on her sister planets. 

 Of these, the first three, in order to be eminently successful, require an accuracy 

 of observation not yet obtained, and the last, while certainly the most reliable of 

 all in its final result, asks for at least five centuries more in which to make a good 

 determination of the distance. In the meantime, the method by observations of 



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