TOPMAN'S OBSERVATIONS OF INGRESS. 43 



After calling the reading 6 r '918 (at 20 h . 45 m . 1 s ) I placed the two images 

 in coincidence to estimate the time remaining before internal contact. This 

 I had frequently practised on the model, and generally was not more than 

 10 seconds in error. I remarked aloud to Mr. Clapp that it wanted a minute, 

 and proceeded to take the two last cusp-measures. Up to this time the circum- 

 stances of the Ingress of Venus exactly resembled those seen in the model. 



I drew out the micrometer at 20 h . 45 m . 43 s without reading it, laid it on 

 the shelf and inserted the negative eye-piece, power 150, down to the pencil 

 mark on it for focus. This I had repeatedly practised on the model, and 

 always effected in 10 or 12 seconds. I was no longer than usual on this 

 occasion. Mr. Clapp watched me, timed me I believe, and noticed that if 

 anything I was quicker than usual. On looking in (at 20 h . 45 m . 55 s therefore) 

 I saw the cusps separated such a distance that I thought it still wanted 

 30 seconds* of contact, but the image not being perfectly sharp I threw it 

 out of focus with the rack motion, and brought it carefully in again. As I 

 did so I perceived that the cusps were united by a narrow band or thread of 

 light of sensible width, but faint, and instantly called " contact," though 

 fearing I had missed it while focussing. This was at 20 h . 46 m . 2 s . As the 

 appearance at that instant made a vivid impression on my mind, I afterwards 

 made a drawing of it (Plate IV., Fig. 1), and may here very properly describe 

 it. The bright parts of the cusps were then far apart; the band of light 

 connecting them merged into them so guadually it was impossible to say 

 where the points of the cusps were. They no longer possessed the sharpness 

 I had seen with the micrometer eye-piece some 20 seconds before. The band 

 of light was of uniform width (calling width the direction perpendicular to 

 the limbs) and of unifor.ni shading for a considerable part of its length 

 between where it merged into the cusps. It was sharply defined along the 

 edge of the planet, but faded off gradually on its other border, where I 

 expected to see the limb of the Sun. Everything hitherto having so closely 

 resembled the appearances in the model, I felt certain that I had missed the 

 contact while focussing, although I could not understand how it could have 

 occurred so much sooner than I had expected. The preceding remarks refer 

 to the instant 20 h . 46 m . 2 s . by the clock. 



Mr. Clapp went on steadily counting the seconds. I was surprised that 

 the band of light did not change much in appearance for some time ; it 

 seemed a long time in comparison with model experience. There was no 



:zr 



V 



* In the note book " 30 seconds " is entered, but in the account which I wrote after the transit I 

 said " 20 seconds." Whether intentionally or not I cannot now tell. It is unimportant. 



a 



