The times given in this book are all based on the sun clock or
a clock adjusted to solar time. It is advisable to have at least
one clock on solar time in order to facilitate the control of one's
sleeping times: Adjust a clock to Greenwich Mean Time (GMT, see
right column). Next, in the case of plus "+" one sets
the minute hand of a clock forward (clockwise) for the indicated
amount of minutes, in the case of "-" the hand is moved
backward. This will show local solar time. To the east of 0° degree
longitude (Greenwich/London) clocks have to be put forward, to the
west, back. For monitoring: 12 noon solar time is always when the
sun is at its zenith! - When in doubt, seek the advice of local
mathematicians, astronomers, etc.
Examples: In Rome the sun clock should be set forward 49 minutes
with reference to Greenwich Mean Time (GMT), in Moscow 2 h. 30 m.,
in Tokyo 9 h. 19 m.; in New York the sun clock should be set back
4 h. 56 m., based on GMT.
Solar (local) time:
As the basis we avail ourselves of 0° degree longitude which runs
through Greenwich near London: The adjustment of the solar clock
proceeds as follows:
1) Set clock to Greenwich Mean Time (GMT):
a) During Winter (from last Sunday in Oct. til last Sunday in March):
Set clock to public time in London/Great Britain = GMT.
b) During Summer (at "Daylight saving time", from last
Sunday in March til last Sunday in October): Set the clock to public
time in London/Great Britain and turn the clock back one hour: your
clock will now show GMT. - For adjustment you can also use Central
European time (MEZ, CET); but public time (= MEZ) in Paris, Berlin,
Rome is always 1 hour ahead of public time in London.
For details: www.timeanddate.com
2) The globe (360° corresponds to 24 hours) is divided into 180°
east and 180° west longitude, 1° degree longitude therefore corresponds
to exactly 4 minutes (12 hours = 720 minutes ./. 180°). At one's
place of residence the clock is put 4 minutes forward (+) per 1°
degree of longitude (east of Greenwich) and 4 minutes back (-) per
1° if one is west of Greenwich.
Example: St. Petersburg is three hours ahead of GMT in Winter. Therefore
the clock is put back three hours to GMT, during "Daylight
saving time" in Summer yet another hour to get GMT.
St. Petersburg lies at 30° 20' longitude east, so (60' = 1°) the
clock is put forward again 30,33 x 4 minutes = 121 minutes (and
32 seconds). Now we have St. Petersburg solar time, which determins
our natural sleeping time!