476 



PHYSICAL SCIENCES. 



NOTE 229, p. 382. Fig. 74 represents the curves in question. It is 

 evident that, for the same focal distance S P, there can be but one circle 

 and one parabola p P R, but that there may be an infinity of ellipses 

 between the circle and the parabola, and an infinity of hyperbolas H P Y 

 exterior to the parabola p P R. 



NOTE 230, p. 387. Let A B, fig. 26, be the diameter of the earth's orbit, 

 and suppose a star to be seen in the direction A S' from the earth when at 

 A. Six months afterwards, the earth, having moved through half of its orbit, 

 would arrive at B, and then the star would appear in the direction B S', if 

 the diameter A B, as seen from S', had any sensible magnitude. But A B, 

 which is 190,000,000 of miles, does not appear to be greater than the 

 thickness of a spider's thread, as seen from 61 Cygni, supposed to te 

 the nearest of the fked stars. 



NOTE 231, p. 389. Stars whose parallax and proper motions are 

 known. 



Name of 



Star. 

 a. Centauri 



61 Cygni .', 

 a. Lyrae .. 

 Sinus 



Arcturus . . 

 Pole Star .. . 

 Capella 

 La Chevre 

 Great Bear 



Proper Motion. 

 .. 3" -764 



'. 5" -123 

 .. 0"-364 

 .. l"-234 

 .. 2" -269 

 0"'035 



0"-461 

 0"-746 



Parallax. 



0"'92 



1" 



0"-374 



0"'207 



0"-230 



0"'127 



0"'106 



0"-046 



0"-046 



0"-133 



Observers and 



Computers. 

 Maclear. 

 Henderson. 

 Bessel. 

 Peters. 

 Henderson. 

 Peters. 

 Peters. 

 Peters. 

 Peters. 

 Peters. 



The space run through in one second by these stars is therefore 



Centauri 

 61 Cygni 

 a. Lyrae .. 

 Sinus . . 

 Arcturus 

 Pole Star 

 La Chevre 

 Great Bear 



5 leagues 

 10 leagues 



Henderson and Maclear. 



leagues 

 22 leagues 



league 

 12 leagues 



7 leagues 



Struve and Peters. 



Henderson and Maclear. 



Peters. 



Lindenau and Struve. 



Peters. 



Peters. 



There are three great discrepancies in the parallax of the star Argelander 

 or 1830 Groombridge. M. Otto Strave makes it 0"'034, which gives it 

 a velocity of 251 leagues per second, while M. Faye finds the parallax to 

 be between 0"*03 and 0"'01, which makes its velocity from 30 to 85 

 leagues per second. 



These are all minimum velocities, because we can only determine on the 

 celestial vault a projection perhaps much foreshortened of the real motions 

 of the stars. 



NOTE 232, pp. 398, 401. The following are the binary systems whose 

 orbits have been accurately determined : 



