TUPMAN'S OBSERVATIONS OP INGRESS. 41 



Mr. Clapp recorded the times from the solar chronometer C, which at 

 2 h . 25 m was 7 m . 55 S> 17 fast on local mean time, and was gaining O'OO per 

 hour (see comparisons, page 62). 



At 3 h . 14 m . 17 s- 5 by the chronometer I first detected the planet entering 

 on the chromosphere. At 3 h . 14 m . 38 s the curvature was so decided I was 

 sure that it was caused by the advancing limb of the planet. At 3 h . 14 m . 47 s 

 I found it difficult to see the red line between the Sun's limb and the planet. 

 At 3 h . 14 m . 56 s I imagined the red line was severed and contact took place. 

 At 3 h . 15 m . 15 s there was a long black division in the middle of the C line 

 which was bright on either side, while the Sun's limb was just visible among 

 the minute irregularities on the edge of the slit. I felt sure that the contact 

 was passed.* 



I then removed the spectroscope and proceeded to the 6-inch equatorial, 

 with which Mr. Nichol had been observing the external contact. Putting in 

 the double-image micrometer and adjusting it as quickly as possible, I made 

 the following measures of the distance between the obtuse cusps, Mr. Clapp 

 counting aloud the seconds from the Equatorial Clock, and recording the 

 observations : 



Equatorial Measures of Obtuse Cusps. 



Clock Times. Micrometer Reading. 



h m s r 



20. 23. 38 4'5g2 



20. 24. 17 4'320 



20. 24. 3g 4'235 



20. 24. 5i 4-200 



20. 20. 12 3'8g5 



20. 25. 28 3-995 



20.25.42 3'7i5 



20. 25. 56 3-696 



It should be remarked here that the integer revolutions of the micrometer- 

 screw were reckoned in one direction only. When the two images coincided 

 and formed but one image, the micrometer-reading was approximately 

 10 r> 000. During the above measures, which are all on one side of the zero, 

 the focussing was slightly imperfect, as I discovered afterwards. The power 

 of the micrometer eye-piece was 250. 



I then removed the micrometer and put in the negative eye-piece, power 

 150, fitted with an achromatised neutral tint wedge. I looked very carefully 

 for any fringe surrounding the planet, and for partial illumination of its disc. 



* The local mean time of External Contact, inferred from the measures of cusps, is 3 h . 8 m . 42" -7 

 which is i m . 41" 9 later than the " spectroscopic " contact. 



