258 COSMOS. 



This lower limit of distances rose to 206265 semi- diameters 

 when certainty to a second was attained in the observations 

 of the great astronomer, James Bradley; and in the brilliant 

 period of Frauenhofer's instruments, (by the direct measure- 

 ment of about the 10th part of a second of arc) it rose still 

 higher to 2062648 mean distances of the earth. The labours 

 and the ingeniously contrived zenith apparatus of Newton's 

 great contemporary, Robert Hooke (1669), did not lead to the 

 desired end. Picard, Horrebow, (who worked out Romer's 

 rescued observations) and Flamstead, believed that they had 

 discovered parallaxes of several seconds, whereas they had con- 

 founded the proper motions of the stars with the true changes 

 from parallax. On the other hand, the ingenious John Michell 

 (PhiL Trans. 1767, vol. Ivii. pp. 234-264), was of opinion 

 that the parallaxes of the nearest fixed stars must be less than 

 0"-02, and in that case could only " become perceptible when 

 magnified 12000 times." In consequence of the widely dif- 

 fused opinion, that the superior brilliancy of a star must inva- 

 riably indicate a greater proximity, stars of the 1st magnitude, 

 as, for instance, Vega, Aldebaran, Sirius, and Procyon, were, 

 with little success, selected for observation by Calandrelli and 

 the meritorious Piazzi (1805). These observations must be 

 classed with those which Brinkley published in Dublin 

 (1815), and which ten years afterwards were refuted by Pond, 

 and especially by Airy. An accurate and satisfactory know- 

 ledge of parallaxes, founded on micrometric measurements, 

 dates only from between the years 1832 and 1838. 



Although Peters, 18 in his valuable work on the distances 

 of the fixed stars (1846), estimates the number of parallaxes 

 hitherto discovered at 33, wo shall content ourselves with 

 referring to 9, which deserve greater, although very different, 

 degrees of confidence, and which we shall consider in the 

 probable order of their determinations. 



w Struve, Astr. stelL, p. 104. 



