¼ of a day to each year, and is rather too much, since the excess of the year above 365 days is not ·25 but ·24224 of a day. The difference is ·00776 of a day, which is the quantity by which our average year is too long. This amounts to a day in about 128 years, or to about 3 days in 4 centuries. The error is corrected by allowing only one out of four of the years which close the centuries to be leap-years. Thus, a.d. 1800 and 1900 are not leap-years, but 2000 is so.
- The day is therefore the first measure obtained, and is divided into 24 parts or hours, each of which is divided into 60 parts or minutes, and each of these again into 60 parts or seconds. One second, marked thus, 1″,3 is therefore the 86400ᵗʰ part of a day, and the following is the
MEASURE OF TIME.4
| 60 | seconds | are | 1 minute | 1 m. | |
|---|---|---|---|---|---|
| 60 | minutes | ” | 1 hour | 1 h. | |
| 24 | hours | ” | 1 day | 1 d. | |
| 7 | days | ” | 1 week | 1 wk. | |
| 365 | days | ” | 1 year | 1 yr. |
- The second having been obtained, a pendulum can be constructed which shall, when put in motion, perform one vibration in exactly one second, in the latitude of Greenwich.5 If we were inventing measures, it