340 CALIFORNIA ACADEMY OF SCIENCES. 



the disk dark or black. Upon again testing with the 120 

 power, the same effect was revealed. The two were moving 

 along, and upon the dark brown-red belt, which has been 

 persistent on Jupiter for some time, and yet they were very 

 markedly black. The shadow was like a drop of ink. The 

 satellite preceded the shadow about 22 minutes of time. 

 The observations were made with the 6 4 inch Equatorial of 

 •the Davidson Observatory. (Clark Objective.) 



The President then read two short memoranda furnished 

 by Messrs. Hill and Burckhalter upon their observations of 

 the black transit of the IV Satellite on the 24th of February. 

 The observation of Mr. Charles B. Hill was made at the 

 Davidson Observatory, and that of Mr. Charles Burckhalter 

 at his observatory in Oakland, and therefore they are inde- 

 pendent observations of the same phenomenon. 



Mr. Hill reports: — "On turning the equatorial on Jupiter 

 about eleven and one-half hours I was surprised to see what 

 was apparently the jet-black shadow of one of the satellites. 

 On looking it up in the Ephemeris to see what satellite it 

 could belong to, I found that the only phenomenon in pro- 

 gress was the transit of IV, the shadow of which should not 

 come on until 15h. 43m., or four hours later, so that this 

 was evidently a " black transit" occurrence. The "seeing" 

 was only moderately good, and as the edges of the planet 

 were not sharp, I concluded there would be no use in wait- 

 ing to observe the time of egress; so after making a sketch 

 of the planet, I closed the observatory and left at 11:50. 

 On the .way down I reflected that it might possibly be the 

 shadow, owing to some erratum in the Ephemeris, and that 

 it would be curious to see whether it would emerge as a 

 satellite or a shadow. I returned, and on getting Jupiter in 

 the field (about 12 h. 10m.) could not at first see the sup- 

 posed shadow at all, but it was finally made out as a dusky 

 spot, only, very near the edge. As before mentioned, the 

 atmosphere was not very good, only permitting the use of 



