The Milky Way 



will appear to us fixed in the sky while the earth 

 is describing its orbit, whereas the nearest star 

 will appear to have moved. We should be 

 therefore able to ascertain for this star an 

 annual oscillation with respect to the small 

 stars. It is, in fact, easy to measure the small 

 angular distance of these adjacent stars: a 

 micrometric screw, enabling the reticule of the 

 telescope to be brought into contact with the 

 stars under consideration, will give their angular 

 distance with an approximation of two or three 

 hundredths of a second. The same degree 

 of precision may be obtained by direct measure- 

 ments from photographs of the group of stars in 

 question. 



Struve, followed by Bessel, developed the 

 details of this method, and to-day the parallaxes 

 of more than fifty stars are known; the pre- 

 cision of these measurements has, in fact, 

 reached such a degree that Kapteyn, the 

 Groningen astronomer, considers it possible 

 to determine the parallaxes of the eight hundred 

 thousand stars contained between the first and 

 the tenth magnitude. We give here, as ex- 

 amples, a few of these parallaxes, with the dis- 



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