SCIENTIFIC SUMMARY. 
95 
and the "best sets of observations. He has thus obtained the following six 
results from the six best methods : — 
Lunar equation of the earth ..... 8". 809 
Lunar parallactic inequality 8". 838 
Micrometric observations of Mars (1862) . . 8". 842 
Meridian observations of Mars (1862) . . . 8". 855 
Transit of Venus 1769 (Powalky’s reduction) . 8 // .860 
Foucault’s experiment on light .... 8".860 
Giving to these results their proper weights, Newcomb obtains as the 
most probable mean 8".848, corresponding to 92,393,000 miles as the sun’s 
mean distance. Leverrier, again, from the method which he considered 
would in the long run supplant all others, deduced the parallax 8". 86. 
Sir G. Airy announces as the result of the British expeditions, so far as 
the Delislean method is concerned (for fortunately many British Halleyan 
observations in the south were made which will be of service when combined 
with similar observations in the north by other nations), a solar parallax of 
8 // .760, corresponding to a distance of 93,321,000 miles, or nearly a million 
miles more than the value regarded by American, Continental, and a large 
number of British astronomers as most probable, and three-quarters of a 
million miles outside the range of probable error in the former evaluation. 
This of itself would show that the Delislean method is as untrustworthy 
as was asserted before the transit. But besides this evidence from the 
comparison of the new result with those before obtained, the results 
themselves on which the new estimate is based show by their wide range 
of discrepancy the unsatisfactory nature of the method of observation relied 
upon by Sir G. Aiiy. The combinations for ingress, which ought to agree 
closely with the observations for egress, differ from them by O'^IOS, corre- 
sponding to a difference of about 1,100,000 miles in the estimated 
distance of the sun. Yet we are gra vely assured that results differing thus 
widely inter se give a mean value which can be trusted as correct within 
200,000 miles. In other words we are to regard Newcomb’s distance based 
on twenty times as many observations by six better methods, as probably a 
million miles too small, and almost certainly 800,000 miles too small, on 
the strength of observations, divisible into two sections, whereof one gives 
a result more than a million miles greater than the result given by the other. 
It is altogether unlikely that astronomers will accept a conclusion of this 
kind. 
Observations of Mars . — Very interesting spectroscopic observations of 
Mars have been made at Greenwich during the recent opposition approach, 
and also many valuable telescopic observations at Madeira by Mr. N. E. Green. 
The spectrum of Mars was compared with that of the moon on August 23 
and September 26, when their altitudes were nearly equal. Several faint 
diffused bands (besides, of course, the dark Fraunhofer lines) were observed 
in the spectrum of Mars on both occasions, of which only the three strongest 
could be seen in the spectrum of the moon. u On September 12,” says the 
report communicated by the Astronomer Royal, “ when the large spot, called 
in Proctor’s chart ‘Dawes’ Ocean,’ occupied the centre of the disc, the 
spectrum of Mars was examined for the detection of local differences. The 
dark spot gave a much fainter spectrum than the rest of the disc, the con- 
