Nebulce — Transits. 443 



gether a peculiarity of vision I am induced to believe from the 

 strange discrepancy that exists as to the colours of a Piscium 

 (see Intellectual Observer, Feb. 1863, p. 55, No. 80). In 

 default of a better explanation, I have thought it possible that 

 in consequence of intense gazing the retina may have become 

 deadened to the blue tint, and consequently would see the star 

 white, but for the complementary orange induced by its being 

 involved in the outstanding blue fringe of its brighter com- 

 panion : this accidental hue in turn disappearing, as the eye 

 recovers itself, to give place to the original blue ; and so on. 

 Mr. Knox agrees with me as to the existence of this 

 fluctuation. 



We must postpone to another opportunity a few more 

 remarks upon this subject. 



CONSTITUTION OF NEBULA. 



Those who have studied one of the most remarkable ques- 

 tions of modern astronomy — that relating to the true nature of 

 nebulas properly so-called — will be extremely interested to 

 learn that from the observations of Mr. Powell, at Madras, 

 there is great reason to infer that the remarkable nebula round 

 the star r\ Argus is gradually but strikingly changing its 

 form and brightness. It is figured in Herschel's Outlines of 

 Astronomy, but is unfortunately not visible in European lati- 

 tudes. We shall now have a renewed inducement to a closer 

 examination of the analogous nebula in Orion, 



TRANSITS OF JUPITER'S SATELLITES. 



July 2nd. Shadow of I. goes off9h. 50m. 8th. Shadow of 

 II. departs 9h. 51m. 9th. Shadow of I. enters 9h. 33m. I. 

 leaves the disc lOh. 38m. 15th. II. goes off lOh. 2m.; its 

 shadow entering 2m. later. 16th. I. enters 10h. 17m. 22nd. 

 II. enters lOh. 8m. 25th. Shadow of I. passes off lOh. 5m. 

 29th. Shadow of III. enters 9h. 19m. 



