M.-P.— Vol. I.] DAVIDSON— APPARENT PROJECTION, ETC. 99 



the image of the whitish, confused, spurious border of the 

 Moon, even when the former is within the latter. The 

 action of the eye is unconsciously selective, but a certain 

 effort of selection is made under the less favorable condi- 

 tion when the star is small or white. There is no effort at 

 selection needed to receive an impression of the Moon's 

 limb, although the actual limb may doubtless be detected, 

 under high powers, inside this factitious border. The im- 

 pression of the image of the star is, therefore, continuous 

 within the range of amplitude of the excursions of the disc 

 of the Moon, but is instantly lost when the limit of this 

 range of vibration is actually reached by the apparent 

 nucleus of the equally unsteady star, and the true limb of 

 the Moon occults it. With a large colored star all the 

 phases of this phenomenon are unmistakable; with a large 

 white star they may be somewhat in doubt, as in the case 

 of 47 Librae and other stars elsewhere quoted ; with a small 

 white star they will probably not be noted, especially in 

 small telescopes with low power. 



The exhibition of the phenomenon at the reappearance of 

 a star on the blurred and factitious bright limb of the Moon 

 should be in exactly the reverse order of the foregoing phe- 

 nomenon of disappearance; and we have been fortunate in 

 looking over our old record to find the original notes of the 

 disappearance of Aldebaran behind the dark limb of the 

 Moon, and its reappearance from the bright limb, on March 

 29, 1887, as elsewhere mentioned. 



In this resume we have confined ourselves to the exhibi- 

 tion of the normal and abnormal conditions in our atmos- 

 phere attending the phenomenon of occultations of stars by 

 the bright limb of the Moon, or by Jupiter or any other 

 planet, because the explanation virtually covers all associ- 

 ated phenomena in solar eclipses, lunar transits, transits of 

 Venus and Mercury, and the vagaries of star images. 



When our atmosphere is absolutely serene there is not 

 and cannot be the slightest abnormal exhibition of form, 

 size, march, or steadiness of images; or of doubt of instanta- 

 neity in the epochs observed. Under such a condition there 



