TEANSIT OF VEima. 109 



after internal contact. The lialo was exactly similar to that seen 

 at ingress, and the whole of the planet at this- time appeared to 

 me intensely black. The halo remained steadily visible for some 

 time, but gradually faded, owing to a great increase in brightness 

 of the atmosphere about the sun ; and at 4h. 6m. 52s. I first 

 observed that the surface of Yenus was not black as it had been, 

 but appeared as if covered with thin, hazy clouds, somewhat 

 thicker on the planet's northern hemisphere. At this time, the 

 haze having much increased, I lost sight of the halo, and at 4h. 

 12m. changed the coloured glass for one of lighter tint, and at 

 once saw the halo again, and for the first time noticed that it was 

 irregular in diameter ; it seemed considerably broader at the 

 north pole of the planet, and shaded off" more rapidly towards B 

 than C (see sketch, diagram 4) , but I found it impossible to look 

 at the sun steadily with this light glass, and again changed it 

 for a darker one, when all the halo, except the part at the north 

 pole, disappeared. This white patch continued visible until within 

 one minute of last contact, and I feel confident I should have 

 seen it some time after last contact but for the rapidly increasing 

 atmospheric haze, which had also much increased on the planet, 

 making it dilficult to see where it ended and the sky began, 



Mr. Lenehan says : — " At 4h. 16m. 21s. the planet a,ppeared 

 with the outer edge apparent, and I noticed a spot of light on 

 the preceding side. It did not appear to me as anything more 

 than a spot." 



Messrs, Belfield and Park saw the following limb of planet at 

 ingress distinctly illuminated, and when the planet was wholly on 

 the sun the body of the planet appeared intensely bluish black in 

 centre, becoming gorgeous deep blue towards the circumference ; 

 at egress the illumination of the planet's limb was again seen, but 

 only on the north side. Mr. Bolding only saw the halo at egress, 

 and though visible all round that part of the planet off" the sun 

 was most marked on the north side. 



It will be seen that we have here three distinct phenomena. 

 A broad ring of light ouside the planet, a bright ring of light 

 round that part of the planet projected on the sky, and band of 

 light or shading round the inner edge of the planet, or over its 

 surface. INo spots, however, were seen on the planet, except the 

 very remarkable part of the halo at the north pole. 



The cause of the halo seen by Messrs. Lenehan and MacDonnell 

 has not been satisfactorily made out, though it has been repeat- 

 edly seen during transits of Mercury. It seems exceedingly 

 improbable that Venus has an atmosphere of such extent as would 

 be required to produce such a halo or ring of light, and if the 

 atmosphere had any density at all similar to that of the earth, 

 the light would be bent inwards, and become too difi'use to be 

 seen long before it reached us. It appears, however, certain that 



