A comet which appeared in 1861 had a very suggestive agreement of orbit when compared with that of the meteors, and the period computed for it was 415 year's.
The problem of determining a heliocentric orbit first presented itself to Kepler, who actually determined that of Mars.
The most plausible explanation of this is that one or more masses of matter move around the sun, whose action, whether they are inside or outside the orbit of Mercury, would produce the required modification in the force.
We begin by considering the laws of motion in the orbit itself, regardless of the position of the latter.
It may be considered as arising from a semi-annual variation in the eccentricity of the moon's orbit and the position of its perigee.
The Solar Astronomical Year Is The Period Of Time In Which The Earth Performs A Revolution In Its Orbit About The Sun, Or Passes From Any Point Of The Ecliptic To The Same Point Again; And Consists Of 365 Days 5 Hours 48 Min.
In any case of a central orbit the hodograph (when turned through a right angle) is similar and similarly situated to the reciprocal polar of the orbit with respect to the centre of force.
The hypothesis which best explains all the phenomena is that the light is that of the sun reflected from an extremely tenuous cloud of particles having the form and extent described, and becoming more and more tenuous as the earth's orbit is approached until, immediately outside the orbit, it fades into complete invisibility.
From the properties of the ellipse, A is the pericentre or nearest point of the orbit to the centre of attraction and B the apocentre or most distant point.
These conditions are: - (I) The smallness of the masses of the planets in comparison with that of the sun, in consequence of which the orbit of each planet deviates but slightly from an ellipse during any one revolution; (2) the fact that the orbits of the planets are nearly circular, and the planes of their orbits but slightly inclined to each other.