TIIE PLANET MAKS IN JANUARY IS67. 
31 
tance of 95,275,000 miles, resulting from observations of Venus 
at her last transits. It is to be noticed that observers proposing 
to take part in investigations of this sort have two methods 
available to them ; the first depending on the difference in Mars’ 
apparent position, viewed (simultaneously) from two distant 
positions on the earth’s surface ; the second requiring no com- 
parison with the work of other observers, but depending entirely 
on the effects of the earth’s diurnal rotation upon the apparent 
path of Mars among the stars. Observers who have sufficient 
skill and suitable instruments should not fail to add their efforts 
to an inquiry of so much interest. It is to be remembered that 
the transits of Venus in 1874 and 1882 may fail to serve us in 
the determination of the sun’s distance. A few days of cloudy 
weather prevailing over two or three regions of the earth’s sur- 
face would leave astronomy to await the next transit, which 
occurs in 1987. 
Since the above was written, I have received one of those 
valuable circulars which are issued at intervals from Mr. 
Bishop’s Observatory. It is prepared by Mr. Hind. I learn 
from it that a determination of the position of the axis of 
Mars founded by Dr. Oudemans upon the observations made by 
Bessel with the Konigsburg heliometer gives results according 
fairly with those of Sir W. Herschel — the assigned inclination 
of the Martial axis being l-i degrees less, however, than Her- 
schel’s estimate. The following numbers may prove serviceable ; 
l means the angle at which the polar axis is inclined (from 
uprightness) towards the earth ; jp means the apparent westerly 
slope of the northern half of the axis (at the time of southing 
on each night: — 
i 
P 
i 
p i 
i 
Jan. 7 
11 11 
o / 
15 12 
Feb. G 
o / 
7 9 
o / 1 
21 17 j 
| Mar. 8 
8 17 
17 
9 25 
17 45 
16 
6 58 
21 52 
18 
9 33 
27 
8 0 
19 52 
26 
7 22 
21 42 
j 28 
11 6 
It will be seen from these numbers that for opposition on 
January 10, the figures of the plate correctly indicate the 
polar presentation of the planet. 
From the same note I find that Leverrier assigns a greater 
diameter to Mars even than that given in Hind’s “ Astronomy ; ” 
since it results from Leverrier’s tabulated apparent diameter 
that he estimates the true diameter of Mars at 5,130 miles. 
This seems to be the estimate lately made use of in the Nauti- 
cal Almanac-, but even with this explanation there remains 
much irregularity, since some of the apparent diameters given 
