528 POPULAR LECTURES AND ADDRESSES. 



Lick Observatory in California. There, at an 

 elevation of 4,500 ft., with an atmosphere of great 

 purity, and with a superb refractor of 36" aperture, 

 they have advantages not obtainable elsewhere. 

 The new satellite is about 112,000 miles distant 

 from Jupiter, and its periodic time is about n h. 

 50 m. Mr. Barnard concludes a short statement 

 of his discovery with the following sentences : 

 " It will thus be seen that this new satellite makes 

 two revolutions in one day, and that its periodic 

 time about the planet is less than two hours 

 longer than the axial rotation of Jupiter. Except- 

 ing the inner satellite of Mars, it is the most 

 rapidly revolving satellite known. When sufficient, 

 observations have been obtained, it will afford a 

 new and independent determination of the mass 

 of Jupiter. Of course, from what I have said 

 in reference to the difficulty of seeing the new 

 satellite, it will be apparent that the most powerful 

 telescopes of the world only will show it" (dated 

 Mount Hamilton, September 21, 1892). 



Sir Robert Ball, in calling my attention to it 

 remarks that " it is by far the most striking 



