rsS IN STARRY REALMS. 



face every time that she is in conjunction. She is usually 

 either over the sun or under the sun, and only on rare 

 occasions have we the pleasing spectacle of a transit of 

 Venus. So rare, indeed are the transits of Venus, that 

 though the present generation has witnessed two, namely 

 in 1874 and 1882, there can be no recurrence of the 

 phenomenon until the years 2004 and 2012 have come 

 round. The Martial inhabitant will also find that a 

 transit of the earth in front of the sun is an occasional 

 and noteworthy spectacle. It has been pointed out by 

 Mr. Marth that such an occurrence might have been 

 witnessed from Mars on the 12th of November, 1879. 



We may, however, for the present purpose ignore this 

 slight inclination of Mars' orbit to our own. But we 

 have now to consider the very different matter of the incli- 

 nation of the axis about which Mars' rotation is performed 

 to that of its actual orbit. We may here again advan- 

 tageously refer to the parallel case of our own globe. 

 The earth, in its annual progress round the sun, turns 

 now one pole and now another towards the sun, thus 

 producing the vicissitudes of the seasons. In a similar 

 manner the equator of Mars is inclined to the plane of its 

 orbit, and thus we sometimes are enabled to see one pole 

 of the planet and sometimes another. It happens that 

 when the planet is in opposition in our autumn, the 

 southern hemisphere is turned towards the earth. The 

 planet is then seen under the most favourable conditions, 

 in so far as its apparent dimensions are concerned ; for, as 

 we have already pointed out, it is under such circum- 

 stances at its least distance from the earth. It thus follows 

 that the most complete series of telescopic pictures of the 



