CALIFORNIA ACADEMY OF SCIENCES. 



339 



BLACK TRANSITS OF JUPITER'S SATELLITES HI AND IV. 



BY PEOF. GEO. DAVIDSON. 



At the meeting of March 3d, 1884, the President called 

 attention to the observation of the black transit of the III 

 and IV Satellites of Jupiter, made by Messrs. Burckhalter 

 and Hill, and himself. The paper was accompanied by his 

 drawings to exhibit the phenomena. 



The first observation was upon the transit of the III Sat- 

 ellite, and its shadow over the disk of the planet, on the 

 15th of January, at 9 hr. 01 m., local mean time, by Profes- 

 sor Davidson. It is illustrated in Fig. 1, wherein the small 

 dark disk is the shadow of the satellite with the partially 

 dark image of the satellite itself three or four diameters to 

 the right. The figure gives the appearance of the planet, 

 etc., as seen with the inverting eye-piece. 



Fig. 1— Jan. 15, 1884— Jupiter at 17h. 11m. G. M. T. 



When it was examined with powers of 120 to 150 diame- 

 ters, the image of the satellite itself showed nearly as dark 

 as the shadow, but not quite so large. After making the 

 first drawing, the atmosphere was steady enough to admit 

 using 255 diameters. This was 12 minutes later, and then 

 the satellite was seen as a circle with a segment of two-thirds 

 of the disk bright white, and the other segment of one-third 

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