40 
POPULAR SCIENCE REVIEW. 
sition.* It will be seen that the planet is nearly as far away 
from tlie earth as it possibly can be at such a time ; but not- 
witlistanding this peculiarity, there are circumstances which 
will render the approaching opposition fully as interesting to 
astronomers as those which occur when the planet is near 
perihelion. 
In the first place, Mars will have a high northerly declination, 
whereas, when in opposition near perihelion, he is far to the 
south of the equator. Accordingly, he will rise fully thirty 
degrees higher above the horizon, and will be seen under pro- 
portionately more favourable atmospheric conditions. 
But, secondly, it has happened that astronomers have paid 
more attention to the planet during those oppositions which 
have occurred when it has been near perihelion ; and the result 
has been that the parts of the planet which will be most favour- 
ably seen during the approaching opposition have not been 
scanned with a sufficiently close scrutiny, and much remains to 
be done by those who wish to aid in delineating the features of 
the planet. P''or there is a considerable portion of the surface 
of Mars which can scarcely be seen at all, save when he is pre- 
sented towards the earth as he will be during the approaching 
opposition and one or two following ones. A reference to the 
paper already mentioned will suffice to show that the southern 
pole of the planet is turned away from the earth when Mars is 
in perihelion ; and although this pole becomes visible when the 
planet is still far from aphelion, yet it is only prominently 
brought forward when Mars is almost exactly in aphelion. Nor 
is this all. The presentation of the same pole towards the sun 
has to be considered. We shall presently have occasion to dis- 
cuss the climatic relations of the planet, and we shall see reason 
for believing that, in many important respects, they resemble 
those of the earth. During the winter season of either hemi- 
sphere, clouds appear to be much more densely aggregated in 
the Martial atmosphere than during the summer season. Hence 
it results that we obtain a far better view of the hemisphere 
which is enjoying the progress of the Martial summer than we 
do of the other. And, as the hemisphere which is bowed down 
towards the earth, at the time of opposition, is also bowed down 
towards the sun, we are not only enabled to obtain a more 
direct view of that hemisphere when so bowed down, but it is 
also the hemisphere which is freest from clouds, and its real 
surface, therefore, is more distinctly visible than that of the 
otlier hemisphere. 
riicro is a error in the position of this line, which should have 
Ixfii further advanced in longitude. A similar error appears in Fig. ,‘3(> 
of Dxrkyer’s “ Le.'imjns in -Vstroiiomy,’' which presents the same relations. 
