TRANSIT OF MEKCURY. 163 
Mr. Conder says—“ I watched the planet at intervals during the 
transit, the definition most of the time being magnificent. The 
sun spots and markings were very distinct, although thin fleecy 
clouds were spread over the whole of the sky. I failed to notice 
any peculiar appearance, except perhaps a very faint suspicion of 
a halo or yellowish light surrounding the intensely black dise of 
the planet, and slightly brighter than the general illumination 
of the sun’s disc. This J attributed to an optical illusion rather 
eo inch ure, an cury 
very indistinct and tremulous,” and he says, “I thought from the 
egress, when near internal contact, : 
difficulty, but fortunately before the actual contact the air got 
steady, and enabled me e ual approach of the limbs 
without the formation of a black drop or haziness. 
7 er any remarks mn these phenomena, I 
Were not troubled with any drop phenomena, while those who had 
bad definition saw more of the drop than they wanted. 
The generally received explanation of the black drop phenomena 
attributes it to irradiation, which gives the sun as seen in our 
false i 
