Ohservatians of the Ti'ansit of Mercury. 183 



observatioQ of external contact would be next to im- 

 possible. 



During the morning hours heliotrope signals were ob- 

 served in conjunction with the Helderberg party, for the 

 purpose of furnishing the Dudley Observatory local time 

 to the latter. These signals were supplemented by powder 

 flashes on the evenings of the 5th and 6th. The necessary 

 details will be found in Mr. Landreth's report appended. 



Although I was on the lookout for the advancing segment 

 of Mercury for fully two minutes before the predicted 

 time of first contact, my attention was so distracted by the 

 constantly increasing and deep rippling waves on the sun's 

 limb, that I saw nothing of the planet until 22^ 18°* 14' 

 D. 0. M. T. ; and at that time the segment was so large 

 that the observation was valueless. 



The record of the first internal contact stands thus : 



Dent times. D. O. M. T. Remarks. 



The time first recorded marks the earliest instant at 

 which I entertained suspicions that internal contact had 

 taken place. Across the dark gap in the sun's limb 

 formed by the disc of Mercury, filaments of light due to 

 atmospheric tremors were continually darting and inter- 

 lacing. I had determined to watch for the instant when a 

 part of these filaments of light coalesced into one un- 

 broken thread, and to regard that as the moment of in- 

 ternal contact. Accordingly, at the second of the recorded 

 times I gave the signal to an assistant, when I had a 

 momentary impression that the light thread had formed ; 

 keeping up the count of seconds, however, it was not 



P 18-° 50^ 



22 20 43.0 



First suspected. 

 Signal given. 

 Internal contact. 

 Contact certainly past. 



18 53 



18 56 



19 05 



46.0 

 49.0 

 58.0 



