...boundary of these two parts is determined by a great circle, the plane of which is perpendicular to the line drawn from the centre of the sun to that of the earth. To this line we suppose the sun's rays to be parallel ; seeing that by reason of the great distance...

...while the planet is going from its perihelion to its aphelion, its motion bcing such that an imaginary line drawn from the centre of the sun to that of the planet, (called the radius vector) deseribes equal areas of the plane of the planet's orbit in equal...

...equator of the earth, in its annual journey, is not always directed towards the centre of the sun? T. I do; twice only in the year, a line drawn from the...it passes through the equator or the tropics, which are circles parallel to the equator, the sun and clocks go together, as far as regards this cause ;...

...while the planet is going from its perihelion to its aphelion, its motion being such that an imaginary line drawn from the centre of the sun to that of the planet, (called the radius vector,) describes equal areas of the planet's orbit in equal times. When...