CALIFORNIA ACADEMY OF SCIENCES. 345 



TRANSIT OF JUPITER'S IV SATELLITE. June 7, 1885. 



[Abstract by Prof. Georgk Davidson of notes of observation by Charles 

 Burckbalter at his Observatory, Oakland. Instrument, 10%-inch Brash- 

 ear reflector]. 



The first observation was at 7h. 20m. local mean time, 

 when the satellite was seen at once as a dark spot on the 

 edge of the north dark belt; about four-fifths of the diame- 

 ter across the disk of Jupiter. Power of eye-piece, 215 

 diameters. Atmosphere too much disturbed for higher 

 powers; definition somewhat fair, but generally unsteady. 

 The satellite exhibited no elongation, although watched for. 

 It was particularly noticed that the north hemisphere of the 

 satellite was apparently the darker. At 8h. 00m. the image 

 was less dark, and it appeared only half its natural size. At 

 8h. 10m. the image was fainter, but in five minutes the 

 steadiness of the atmosphere improved, and the satellite was 

 distinctly visible but not very sharply defined. It gradually 

 got fainter as it entered the blurred limb of the planet. 

 Before egress, and for some minutes after predicted time of 

 egress, the satellite was invisible; when it reappeared it was 

 as a bright spot or projection outside the limb of Jupiter. 

 Atmosphere too disturbed to judge of the elongation of the 

 image of the satellite. 



"& v 



At 9h. 04m., the satellite being off the planet's limb, the 

 the observer particularly noted that the satellite was north 

 of the north dark belt; so that it would appear as if the 

 satellite is divided into bright and dark areas, the south pole 

 being the dark one. 



The satellite was barely visible and exceedingly small, 

 and when clear of the planet's disk it was about one-sixth 

 of the brightness of Satellite II. It gradually grew brighter, 

 and at 9h. 15m. it was about one-third as bright as Satellite 

 II. 



