HOGGAN'S OBSERVATIONS OF THE TRANSIT. 397 



The planet when on the Sun's disc appeared of a perfectly circular form, 

 and there was no appearance of refracted light round its edge, which was 

 very sharp, the whole body of the planet being intensely black. 



In the original record of the observation of Ingress all the phenomena 

 attached to the times were registered instantly by Lieut. Moore, with the 

 exception of the important phenomenon of circular contact at 6 h . 34 m . 4 Sl 8, 

 and the less important phenomena attached to the times 6 1 '. 33 m . 36 s -2 (re- 

 garding which time there is a correction on the left-hand side of the page 

 to 6 h . 33 m . 56 s -2, to which Lieut. Moore's initials are appended), 6 h . 36 m . 7 3 '9, 

 and 6 h . 36 m . 17 S> 4, which were written by myself, from memory, immediately 

 after. 



The pocket chronometer Parkinson and Frodsham was used for recording 

 the times of the observation of Ingress. It was compared, both before and 

 after Ingress, with the other two chronometers, Hewitt and Cotterell. 



Lieut. Moore devoted the interval between Ingress and Egress to obser- 

 vations of the altitude of the Sun, for the determination of local time. 



Note by the Astronoiner Royal. 



The remark made by Lieut. Hoggan, on the trifling character of the 

 change of phenomena between 6 h . 34 m . 57 s . and 6 h . 36 m . 7 S> 9, throws a doubt 

 on the accuracy of the observation. 



It seems possible that at 6 h . 33 m . 17 8 '5, 6 h . 34 m . 4 s -8, 6 h . 34 m . 16 s , 6 h . 34 m . 57 s , 

 10 h . 3 m . 18 s -2, 10". 3 m . 51 s , 10". 3 m . 56% and 10". 4 m . 47 s , the minute may have 

 been registered l m . too small ; while at 6". 36 m . 7 S> 9, 6 h . 36 m . 17 S> 4, 6 h . 36 m . 32 S> 8, 

 and 6 h . 36 m . 43 S> 2, it was registered correctly. 



These changes of several numbers appear to reconcile the observations at 

 Hermitage Island with other observations in Rodriguez. 



Errors may sometimes be caused by noncoincidence of the minute-hand 

 with the minute-line when the second-hand points to 60. It was, however, 

 an Official Instruction to the Assistant who should read the clock or chrono- 

 meter, " It is desirable that he assure himself of the correspondence of 

 indications of the minute-hand and the second-hand." 



Observation of Egress. 



About twenty minutes before internal contact at Egress, the chronometers 

 being intercompared, I commenced observing the planet. 



The observation of Egress was made under the most favourable circum- 

 stances. The Sun's limb and the planet's limb were both very sharply 



