178 The Planet Mars in 1873. [April, 



number of atolls and the thickest reefs occur south of the 

 equator; (2) That the north-temperate forms of life in 

 equatorial regions greatly exceed the south-temperate forms. 

 10. The general conclusion from these facts seems to be, 

 that the northern hemisphere suffered glaciation at the latest 

 period, and that the southern hemisphere was glaciated at 

 a time perhaps more remote from the period of the northern 

 glaciation than that is from the present. 



IV. THE PLANET MARS IN 1873. 



By Richard A. Proctor, B.A. (Cambridge), 

 Honorary Secretary of the Royal Astronomical Society. 



tHE planet Mars, after being unfavourably placed for 

 observation during two years, has returned to a 

 position where he can be studied advantageously. On 

 April 27th he will be in opposition, and therefore due 

 south, or at his highest above the horizon at midnight. 

 Then, also, he will present his largest apparent disc, or 

 very nearly so (at least so far as the present opposition is 

 concerned). Moreover, as will be seen farther on, there are 

 circumstances which render the study of the planet while in 

 our neighbourhood particularly interesting on this occasion. 

 Therefore the opportunity seems a favourable one for 

 entering into the consideration of the various facts of interest 

 which have been made known respecting Mars. But in- 

 asmuch as I have on more than one occasion discussed the 

 principal features of the planet, I shall here restrict myself 

 as far as possible to circumstances presenting some degree 

 of novelty, and devote much of my space to the suggestion 

 of observations which should be made by telescopists daring 

 the next two or three months. 



It will be known to most of my readers that the planet 

 Mars is the only primary member of the solar system whose 

 condition can be studied under circumstances sufficiently 

 favourable to enable us to arrive at satisfactory conclusions 

 respecting the planet's physical condition. Venus approaches 

 us more nearly, and is more brilliantly illuminated ; but 

 when Venus is at her nearest she lies directly towards the 

 sun, and her unillumined side is turned towards us. She 

 is more favourably seen when near her elongations, but is 

 then much farther away than Mars at his nearest, at which 

 time he (unlike Venus) is most favourably situated for obser- 

 vation. Moreover, the great brightness with which Venus 



