x THE STARRY HEAVENS 413 



earth's orbit we can calculate the distance of 

 the star. The difficulty is that the apparent 

 ellipses are so minute that it is in very few 

 cases possible to measure them. 



Jan. 



July 



Fig. 54. The Parallactic Ellipse. 



The distances of the Fixed Stars thus tested 

 are found to be enormous, and indeed gener- 

 ally incalculable ; so great that in most cases, 

 whether we look at them from one end 

 of our orbit or the other though the dif- 

 ference of our position, corresponding to the 

 points marked January and July in Fig. 54, 

 is 185,000,000 miles no apparent change of 

 position can be observed. In some, however, 

 the parallax, though very minute, is yet ap- 



