236 
POPULAR SCIENCE REVIEW. 
we have not any complete account of the observations made by 
Schroter, W. Herschel, De la Hue, Dawes, and a host of other 
observers, but only a few fragments here and there. I venture 
to say that the work done by Dawes alone upon Mars, if it had 
been brought together by himself and published as a book, 
would have done more to throw light on the planet’s condition 
than such scattered selections from the labours of a dozen of the 
best observers (including himself) as are alone available to us 
under the present system. 
It will be well, before proceeding to consider the features 
to which telescopists should direct their attention during the 
approaching opposition of Mars, to note the order in which 
favourable and unfavourable oppositions of Mars succeed each 
other. The coming opposition, as most of my readers doubtless 
know, is one of the most favourable of the present century. 
The planet will not be quite so near to perihelion, at opposition, 
as he was in 1845 (when, by the way, many observations of 
interest were made) ; but he will be more favourably situated 
for observation in our northern hemisphere, because of his less 
southerly declination. In 1830 he was more favourably placed 
in this respect (being nearly on the equator at opposition), but 
further from perihelion. In 1892 he will be at once further 
from perihelion and less favourably placed. These oppositions . 
(1830, 1845, 1877, and 1892) are the nearest to perihelion 
during the present century ; after them come, in order of dis- 
tance, 1862, 1860, 1847, 1879, 1875, 1864, 1890, and 1881. 
It is easy to ascertain the circumstances which determine 
the recurrence of oppositions in favourable and unfavourable 
positions. 
The sidereal period of the earth being 365*2524 days and 
that of Mars 686*9797 days, in order to determine the varying 
position of oppositions we must in the first place consider the 
improper fraction and, presenting it as a continued frac- 
tion, obtain from it a series of fractions approaching it more 
and more nearly in value. (The remainders obtained in this 
process all represent the number of days by which various mul- 
tiples of the sidereal year and the sidereal period of Mars differ 
from each other.) We obtain : 
6,869,797 
3,652,524 
i 1 1 1111111 JL 111111 
+ i + 7+ 2+ 1+ 1+ 3+ 1+ 1+ 7+ 1+ 6+ 2+ 5+ 3+ 1+ 3‘ 
(I commend the prevalence of l’s, 3’s, 7’s, and 2’s in this- 
result, and the absence of 4, 8, and 9, to the special attention 
of all who find strange significance in the excess of 3’s and the 
