MARS IN THE AUTUMN OF 1877. 
239 
ticular method of determining the sun’s distance in Chapter I. 
of my treatise on the Sun. I believe it will be found that the 
observations to be made next September by this method will 
afford measures of the sun’s distance comparing favourably with 
those obtainable by any other methods, including the observation 
of Venus in transit. It is unfortunate that official astronomers 
in this country have not endeavoured to obtain the sanction of 
Government for any expeditions by which advantage could be 
taken of the near approach of Mars. But it must be remem- 
bered that, being themselves in the receipt of money from 
Government, they naturally feel some delicacy in advocating 
the outlay of Government money on the observations of special 
phenomena outside the routine of work in the public observa- 
tories. It is understood, too, that apart from any question of 
delicacy, Government observers have lately had good reason for 
avoiding any suggestions in favour of expenditure on scientific 
expeditions, very plain hints having been given them that it does 
not fall within the duties of their office to make such suggestions. 
Be this as it may, it is certain that the only expedition for 
observing the approaching opposition of Mars is one undertaken 
by Mr. Gill, who managed very successfully the heliometric 
observations of the transit of Venus at the Mauritius (Lord 
Lindsay’s transit expedition). For this expedition a sum of 500£. 
has been provided by the Astronomical Society, and the fine 
heliometer used in 1874 has been lent by Lord Lindsay. 
The observation of the features of the surface of Mars, though 
not a task of equal difficulty, is one of nearly equal scientific 
importance. Whether the Sun is a few hundred million miles 
nearer to us or farther from us than had been before supposed, 
is in reality a matter of very little moment. The exact de- 
termination of the Sun’s distance, if it could be effected, would 
not have the least practical value, and in this sense would not 
be one whit better than the determination of the true shape and 
position of the lands and seas of Mars. There is a meaning, in- 
deed, in every change in our estimate of the Sun’s distance, which 
is full of interest for the student of nature ; but surveying as- 
tronomy, so to describe the work for which Government ob- 
servatories are established, could get on quite as well if the 
Sun’s distance were erroneously estimated by many millions of 
miles, as if we knew the distance to a hair’s breadth. Certainly 
the determination of the physical features of a planet is not 
devoid of interest for the student of science ; it enables us to 
judge of the planet’s actual condition, to compare the planet 
with our earth, to draw inferences respecting the influence of a 
planet’s size, mass, and position on the progress of those various 
changes which constitute the life-history of the planet. Indeed, 
I do not hesitate to say that if we could obtain exact knowledge 
