184 Remarks on the Dudley Observatory 



until the third time above recorded that I felt couMent 

 thatinternal contact was eflected. Mne seconds later, there 

 was no longer the slightest doubt. 



I had (previously to the transit) formed the opinion, from 

 a careful consideration of the experience of others, sup- 

 plemented by theoretical considerations, that it is important 

 that the observer of an internal contact should ignore as 

 much as possible the phenomenon as a whole, and devote 

 his attention as exclusively as possible to the expected 

 point of juncture of the advancing cusps. In addition to 

 this he should be provided with a high magnifying power, 

 since the matter of distinct definition is, in this case, not 

 highly important. In fact it appears to me that the re- 

 quirements of this case bear a close analogy to those in- 

 volved in the detection of a faint and moderately close 

 companion of a bright star. 



The definition could not well have been worse than in 

 the observation just recorded. Under the circumstances 

 and viewing the phenomenon as a whole with a low power, 

 I am. convinced that the apparent uncertainty would have 

 been at least 20 or 30 seconds; as it was I felt that the 

 phenomenon as shown in my telescope under all the dis- 

 advantages was not uncertain more than 5 seconds. I had 

 fully intended to use a power of 500, under good atmo- 

 spheric conditions. 



Principally through the kindness of the respective ob- 

 servers I am able to present a comparison of the Dudley 

 Observatory times of contact with a few others. Using 

 the data of the American Ephemeris, except that the semi- 

 diameter of the sun is assumed to be (with the Berlin 

 Yahrbuch), 16' 1 find after a tolerably rigorous com- 



putation the predicted Washington times of contact for a 

 given place in longitude, \ west from Washington and in 

 north geocentric latitude cp' to be : 



