One can see further that as one goes south to lower latitudes, the variation of the length of the day is weaker, so that the Equation of Time is more successful in pushing the date of earliest clock time of sunset forward in the month of December conversely in high latitudes getting near the Arctic Circle the natural Sun Time and Star Time variation in the length of the day No difficulty was experienced until accurate clocks were constructed, when: it was found that the interval between midday and midday judged by the sundial is not always the same length of time judged by the clock. "The sun is sometimes early and sometimes late on the perfect clock.
The same is.not true of the stars, however. If there was a star bright enough to cast a shadow on a sundial, the interval between successive indications of 12 o'clock star time would agree perfectly with equal intervals on a mechanical clock—but the intervals would not be days. This is because the earth goes round the -sun in such a sense that, as it turns on its axis 366% times in one year, the revolution round the sun makes the sun appear to rise and set once less or 36844 times per year. Hence there are 365% ordinary days and 366% side real days in a year, and the side real day is. about 4 minutes shorter than the solar day.
It is no good using side real time for civil purposes, because 6 o'clock side real time occurs im the evening in the autumn, at midday in winter, in the early morning in spring and at midnight in summer. If we kept side real time on our clocks we should be faced with the choice of having the morning bus to town (if and when it keeps time) running 4 minutes later each day, or of following the indicated time and lunching at midnight at some time of the year. We prefer, of gblrse, to take no notice of astronorhical, nonsense, to use a time which agrees more or less with solar time, but to keep it on perfect mechanical clocks and to disregard the fact that 12 o'clock clock time is not always 12 o'clock sundial time.
Equation of Time The difference between ¿sundial time and civil time is called the eqution of time. It is quite large. On January 1, solar time is 3 minutes behind civil time; in the first week in February, it is 14 minutes behind; on April i6 they coincide, and by May 16 solar time has got.3% minutes ahead. From this date however it falls back, the two time systems being coincident on June 14, Late
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in July the solar time is 6 minutes behind civil time, and it starts to gain again, its biggest lead being 16 minutes 22 seconds on November 4. From this date until February. solar lime loses on civil time.
We can now see why the equation of time comes into our correspondents question. Midday by the sundial occurs at 1144 am. on November 4, at 1L51 am. on December 1, at 11.58 am. on December 21, and at noon on Christmas Day. If the sun always set six hours after noon sunset would move from 544 pin. on Bay, that is today, on account of the "November 4 to 6 pin. on Christmas
Text read from the printed page and cleaned; old type leaves the occasional error.