260 



PROCEEDINGS OF THE AMERICAN ACADEMY 



telescope was mounted on an equatorial stand obtained from the Messrs. 

 Blunt of New York. The instrument was mounted in the parapet of 

 the castle, and was placed for shelter against the wind under the lee 

 of the north wall of the upper tier The interior contact of the planet 

 at ingress had passed before the instruments were ready for use, on 

 account of some unexpected difficulties which delayed the preparation. 

 An observation was taken of the time when the second limb of the 

 planet had passed within the sun to an extent equal to its own diameter, 

 as nearly as the eye could judge. The correct or reduced sidereal 

 time, as noted by the sidereal chronometer (No. 2419), was 2''- 35'"- 

 25'". The correct or reduced mean time, as noted by the mean solar 

 chronometer (T. Dallas 158), was 11''- 29 " 59'-.9, civil account. 

 The transit, at the egress of the planet, was observed with great satis- 

 faction. For this purpose the instrument was removed from the para- 

 pet, and placed on a large flat slab of granite standing on the ground. 

 It was first observed when the planet was within the sun's disc by a 

 space equal to its own diameter. The time by the sidereal chronometer 

 was 8"- 5r- 26^-, and by the solar chronometer, S*"- 47™- 58".4 P. M. 

 The next observation was on the interior contact. The time was sat- 

 isfactorily observed to be 8^- 57™- 30'-.7 sidereal time, and 5" 51™- 

 3'-. 2 solar time. Immediately after this observation, perhaps two 

 seconds of time, the whole disc of Mercury, appearing perfectly round, 

 seemed to be within the sun's disc again. There was an apparent 

 connection between the limbs of the sun and Mercury by a little black 

 stem of the same color as the planet. This stem appeared, when 

 first seen, as long as one fifth or one sixth of Mercury's diameter. 

 It remained distinct for thirty-three seconds of mean time, when, by 

 a gradual diminution, it disappeared ; thus forming a second apparent 

 internal contact, at 8"- 58'"- 6' A sidereal time, and 5^- 51™- 38\4 

 solar time. The disappearance of the planet from the sun's disc 

 was watched with great satisfaction and distinctness, until it became 

 like the finest black dot hanging on the exterior edge of the sun. The 



total disappearance took place at 9''" O™- 59',6 sidereal time, and 

 5h. 54m. 3p.^ ^^^^ g^jgj. ^j^^g^ 



" The chronometers were regulated by equal altitudes of the sun, 

 taken on the 7th and 8th of May, with an eight-inch sextant made by 

 Troughton and Simms, and an artificial horizon sheltered by a glass 

 roof in the usual way." 



The Corresponding Secretary read a letter from the As- 



