198 Remarks on the Dudley Observatory 



segment of about 20° of the sun's limb cut off for its re- 

 ception by an oblique micrometer wire, and my vision was 

 directed to that point at the instant of appearance, the 

 sun's limb appearing beautifully steady and sharply de- 

 fined. 



At instant just preceding internal geometrical tangency 

 at Contact II, there darted out from each cusp a thread 

 of light and closed instantaneously about the planet, forming 

 for the instant a slight protubrance on the sun's limb. 

 The instant of the occurrence of this phenomenon is that 

 designated as phase (e). 



The same phenomenon, though in a reverse order, ap- 

 peared at egress, except that concerning the momentary 

 existence of the prominence I could not be certain, owing 

 to the greater unsteadiness of the sun's limb ; but in both 

 instances nothing could be imagined more sudden than 

 the flashing together and the dividing of the thread of 

 light between the planet's and sun's limb ; possibly ap- 

 pearing more remarkable to me as I was prepared not to 

 be surprised at seeing a " black-drop." 



Concerning the physical features sought during transit, 

 the almost uninterrupted cloudiness of the sky which pre- 

 vailed from II to III, prevented any extended examina- 

 tion of the planet, but at 23** 00"" the existence of a small 

 illy-defined light spot near the center of Mercury's disc 

 was suspected, and the suspicion was afterwards repeatedly 

 verified by both Mr. Wilson and myself. It appeared in 

 form slightly elongated or more properly pear-shaped ; in 

 position a little to the east and, as estimated, north of the 

 center of the disc. 



I am convinced that if this appearance must be decided 

 to be an optical illusion, as seems most probable, it must 

 still partake of the character of something more than an 



