708 



OCCULTATION OF VENUS, 



as to place the moment of internal contact in doubt by five or six seconds, 

 and to cause the rejection of all observations of this phase in computing the 

 Solar Parallax. From this occultation of Venus, I feel sure that no part of 

 that effect can be due to the Solar Corona; but must be ascribed either to 

 irradiation and diffraction or to the disturbing effect of the atmosphere of 

 Venus. The phase of external YSp" 1 



contact, which could not be ob- 

 served by the unaided eye, is il- 

 lustrated in Diagram No. 1. It 

 marks the beginning of partial 

 phase at immersion. The curve 

 of the Moon's dark limb, pro- 

 jected on the bright semi-circle 

 of Venus, now rapidly advanced 

 towards the straight line or di- 

 ameter, dividing the enlightened 

 and unenlightened halves. This 

 line is called the Terminator, and 

 is marked by the letters n, s, in 

 all the figures. In 31.11s. (seconds), the curve reached the northern point 

 'Or eusp^of the planet, as shown in Diagram No. 2. This cusp was simply 

 Hunted, but there was no disturbing tti q 



arc of light, and the time was in- ° 



stantaneously noted, at 22,h, 48m. 

 46.63s. Gl. Sid. time, or 5/i. 37??i. 28.2s. 

 Gl. mean time. JSTow began the 

 most interesting part of the phe- 

 nomena. As the arc advanced, the 

 curve cut off more and more of the 

 isie-ctor-like surface yet illuminated. 

 But 18.99s. now remained, and in 

 that brief space there was much to 

 see. They were moments of intense 

 excitement, as I watched that tri- 

 angular surface of light, bounded 

 by two curves and a straight line, 

 gradually fading into nothingness. 



In figure 2, I have drawn the arc I a, to mark the position of the Moon's 

 limb and the rapidly vanishing surface of light, but six or eight seconds 

 before the beginning of total phase. In a few seconds more the southern 

 cusp shot out its last ray and Cynthia had vanquished Venus. See Diagram 

 No. 3. This instant was noted at 22/i. 49m. 5.6s. Gl. Sid. time, correspond- 

 ing to 5A. 37m. 47.14s. Gl. mean time. At this time however, all the dark 

 iune of Venus, bounded by the curves m s and m v s, was still projected 

 beyond the Moon's "ashy limb." 



