quarters, that is, from Cancer to Libra, and from Capricorn to Aries, the sun is faster than the clocks, and while it is travelling the other two quarters it is slower.

Tutor. Just so: because, while the earth is travelling through the second and fourth quadrants, equal portions of the ecliptic come sooner to the meri dian than their corresponding parts of the equator: and during its journey through the first and third quadrants, the equal parts of the ecliptic arrive later at the meridian than their corresponding parts of the equator.

James. If I understand what you have been saying, the dial and clocks ought to agree at the equinoxes, that is, on the 20th of March, and the 23d of September; but if I refer to the Ephemeris, I find that on the former day [1822) the clock is almost

8 minutes before the sun; and on the latter day the clock is almost 8 minutes behind the sun.

Tutor. If this difference between time measured by the dial and clock depended only on the inclination of the earth's axis to the plane of its orbit, the clocks and dial ought to be together at the equinoxes, and also on the 21st of June and the 21st of December, that is, at the summer and winter solstices; because, on those days, the apparent revolution of the sun is parallel to the equator. But I told you there was another cause why this difference subsisted.

Charles. You did: and that was the elliptic form of the earth's orbit.

Tutor. If the earth's motion in its orbit were uniform, which it would be if the orbit were circular, then the whole difference between

equal time as shown by the clock, and apparent time as shown by the sun, would arise from the inclination of the earth's axis. But this is not the case, for the earth travels, when it is nearest the sun-that is, in the winter, more than a degree in 24 hours, and when it is farthest from the sun, that is, in summer, less than a degree in the same time: consequently from this cause the natural day would be of the greatest length when the earth was nearest the sun, for it must continue turning the longest time after an entire rotation, in order to bring the meridian of any place to the sun again; and the shortest day would be when the earth moves the slowest in her orbit. Now these inequalities, combined with those arising from the inclination of the earth's axis, make up that differ

ence which is shown by the equation table, found in the Ephemeris, between good clocks and true sun-dials. There is another cause arising from what astronomers call the equation of precession in right ascension; but its effects are very small, and the explication is too intricate to be introduced

now.

CONVERSATION XIII.

Of Leap-Year, aud the Old and New Styles.

JAMES. Before we quit the subject of time, will you give us some account of what is called in our Almanacs Leap-year?

Tutor. I will. The length of our year is, as you know, measured by the time which the earth takes in performing her journey round the sun, in the same manner as the length of the day is measured by its rotation on its axis. Now, to compute the exact time taken by the earth in its annual journey, was a work of considerable difficulty. Julius