continuing to 23h 59m. It is used by astronomers, chiefly to express in hours and minutes of
sidereal time the Midheaven longitude of a given place. Prior to 1925 0h of the astronomical
day coincided with noon but in that year astronomical and civil time were made to coincide,
since when oh has coincided with midnight.
Solar Time. That in which the point of reference is the Sun. This may be apparent Solar time,
as shown by a sundial; or local Mean Time, as shown by a clock adjusted to an average rather
than an actual day. This is explained more fully under Equation of Time (q.v.). With Solar
Time, noon was approximately four minutes earlier or later with every increase of distance of
1° East or West of Greenwich Observatory, which at zero longitude is the point for which
Universal or World Time is computed. Apparent and Mean Solar Time coincide four times a
year: on April 15, June 14, Sept. 1 and Dec. 25. At all other times the Sun is fast or slow by
from one to sixteen minutes.
Standard Time. Since the meeting of train schedules is impossible on the basis of local time,
Standard time-zone meridians were spaced at intervals of 15° of longitude East and West of
Greenwich, and all clocks within each zone were adjusted to the mean Solar time of the
midpoint of the zone. Standard Time was generally adopted on Nov. 18, 1883, but it did not
come into common use in some localities until after many years had elapsed. Even yet there
are communities in which the time of day is given in Sun time; unless you wish to catch a
train, in which case you are given Railway Time. Not only that, but longitude is becoming an
increasingly unreliable guide, for some communities which are actually in the Central
Standard Time zone run by Eastern Standard Time, to make their business day coincide with
that of some nearby city across the meridian; and similarly at various points throughout the
world. Lacking such exceptions, all places in the United States east of 82°39' W. Long. are
theoretically in the Eastern Standard Time zone, and their time is 5h earlier than that of
Greenwich; Central Standard Time, 6h earlier than Greenwich, applies to points between 82°
30' and 97°30' W. Long.; Mountain Standard Time, 7h earlier than Greenwich, between 97°
30' and 112°30' W. Long.; and Pacific Standard Time, 8h earlier than Greenwich, to all points
in the United States west of Long. 112°30'. However, one need but observe on any time zone
map the irregular lines which indicate the Time Zone meridians across the country, to realize
how important it is that any statement of time of an event is incomplete and unreliable unless
it carries with it a statement of the kind of time in which the event was recorded, and the
standard meridian adopted by that community.
Daylight Saving Time. This was originated in England in 1916, where it was called Summer
Time. It consists of an arbitrary setting ahead of the clock by one hour, thereby shifting all the
day's activities an hour earlier, ending the work day that much sooner and leaving an hour
more of daylight in which to indulge in seasonal recreations. In general, it commences at 2 A.
M. of the Sunday following the third Saturday in April, and ends on the Sunday after the first
Saturday in October. This is not a reliable guide, for in its earlier years it sometimes began as