346 POPULAR SCIENCE MONTHLY. 



to mention that, in addition to Titan and Japetus, the satellite 

 named Khea, the fifth in order of distance from the planet, is not a 

 difficult object for a three- or four-inch telescope, and two others 

 considerably fainter than Khea — Dione (the fourth) and Tethys 

 (the third) — may be seen in favorable circumstances. The others 

 — Mimas (the first), Enceladus (the second), and Hyperion (the sev- 

 enth — are beyond the reach of all but large telescopes. The ninth 

 satellite, which has received the name of Phcebe, is much fainter 

 than any of the others, its stellar magnitude being reckoned by 

 its discoverer at about 15.5. 



Mars, the best advertised of all the planets, is nearly the least 

 satisfactory to look at except during a favorable opposition, like 

 those of 1877 and 1892, when its comparative nearness to the earth 

 renders some of its characteristic features visible in a small tele- 

 scope. The next favorable opposition will occur in 1907. 



When well seen with an ordinary telescope, say a four- or five- 

 inch glass. Mars shows three peculiarities that may be called fairly 

 conspicuous — viz., its white polar cap, its general reddish, or or- 

 ange-yellow, hue, and its dark markings, one of the clearest of 

 which is the so-called Syrtis Major, or, as it was once named on 

 account of its shape, " Hourglass Sea." Other dark expanses in 



the southern hemisphere are 

 not difficult to be seen, al- 

 though their outlines are 

 more or less misty and indis- 

 tinct. The gradual diminu- 

 tion of the polar cap, which 

 certainly behaves in this re- 

 spect as a mass of snow and 

 ice would do, is a most in- 

 teresting spectacle. As sum- 

 mer advances in the south- 

 ern hemisphere of Mars, the 

 white circular patch sur- 

 rounding the pole becomes 

 ^ , „ smaller, night after night, 



Mahs seen with a Five-Inch Telescope. ' •= , <=> ' 



until it sometmies disappears 

 entirely even from the ken of the largest telescopes. At the same 

 time the dark expanses become more distinct, as if the melting of 

 the polar snows had supplied them with a greater depth of water, 

 or the advance of the season had darkened them with a heavier 

 growth of vegetation. 



The phenomena mentioned above are about all that a small 

 telescope will reveal. Occasionally a dark streak, which large in- 



