TRANSITS OF THE II AND III SATELLITES OF JUPITER. 89 



TRANSITS OF THE n AND IH SATELLITES OF JUPITER. 



By George Davidson, U. S. Coast and Geodetic Survey. 

 [Davidson Observatory, March 20th, 1886.] 



About three o'clock in the morning of Sunday the 21st, I 

 watched the transits of the II and III Satellites of Jupiter 

 and their shadows. The shadow of the II Satellite was on 

 the northern edge of the northern dark belt, but it was in- 

 tensely black; the image of the satellite was probably a 

 diameter from the shadow but was in the edge of the white 

 part of the planet. This image was more than white; it was 

 a hrilliant ivliite. The image of the III Satellite was yet three 

 or four diameters outside the planet's limb; a few minutes 

 before its first contact therewith the black image of the shadow 

 of II was not so conspicuous as it had been, for I picked out 

 the bright image of the satellite before seeing the dark 

 shadow. I was using a power of 150 diameters. 



About the time of the first contact of III, the sky became 

 slightly hazy and I did not get the time of the contacts of 

 the shadow with the planet's limb. After the shadow of 

 the III Satellite was on the disc of the planet, and just after 

 the first contact of III as a white image, the image of II 

 became too faint to be certain of my seeing it. 



The haziness or light fog increased, and the planet was in- 

 visible to the naked eye, but occasional thin openings through 

 the mist enabled me to see III and its shadow after both were 

 certainly on the disc of the planet. For seven minutes after, 

 the white' image was brighter than the body of the planet; both 

 the shadow and image were transiting the disc where it was 

 moderately clear of dark lines; ^^et the shadow was travers- 

 ing the northern edge of a faint one. In fifteen minutes 

 after the second contact, I noted the shadow of III, but 

 could not see the image of the satellite. At twenty-three 



7— Bull. Cal. Acad. Sci. II. 5. Issued Aug. 31, 1886. 



