5.5 France and the International Organization of Science
81
creasingly necessary to coordinate times and clocks internationally. Until then,
everyone used their own local time, related to the local geographical longitude,
in which the clock was basically set in such a way that on average throughout
the year the Sun was exactly in the south at noon. I digress briefly in order to
explain why I used the wording ‘on average’. It is not that simple in practice,
because there is the so-called ‘equation of time’, which is the property of the
Sun to be on the meridian too early or too late relative to the clock. This
difference varies in the course of a year. Its cause is that the Earth in its orbit
around the Sun does not have a constant speed and also because the rotation
axis of the Earth is not perpendicular to that orbital plane. The difference can
be up to 18 minutes, but of course averages out over a whole year. This can
be seen in the analemma, the distorted figure eight that is often depicted on
old maps and sundials. It shows up when we take a photograph of the Sun in
the sky every day at exactly the same time on the clock; if this is done for a full
year on a single plate, then the images of the Sun on it form this figure. The
vertical, long axis of the analemma is created by the seasons, which makes the
Sun high in the sky in the summer and low in the winter; the horizontal axis
by the equation of time.
In order to achieve greater uniformity, the idea had been put forward to
divide the Earth up into 24 zones of 15 ◦ in geographical longitude, whereby
the time within each zone would be the same everywhere and would differ by an
hour from the zones next to it. For practical reasons the zones were not chosen
as exactly 15 ◦ , but national borders were used. This system had originally
been proposed in 1879 by Sandford Fleming (1827–1915), a Scottish-born
Canadian engineer, but was also suggested by others independent of him. The
question was then where the meridian would run that would define longitude
zero. In October 1884, after long and bitter discussions, the decision was
made in Washington. The zero meridian ran through the Royal Observatory
in Greenwich and not through l’Observatoire de Paris. This ‘defeat’ was difficult
to accept for the leader of the French delegation, the astronomer Pierre Jules
César Janssen (1824–1907).
The Netherlands (and France and most of western continental Europe) are
in the the Central European Time zone, one hour later than Greenwich Mean
Time (nowadays called Universal Time). For the Netherlands the current situation actually is less favorable; on average (except for the equation of time) the
Sun is in Utrecht—for example, more or less the center of the Netherlands—on
the meridian at 12:39:32 (and one hour later during Daylight Savings Time).
Had the French been given the zero meridian, it would have been 11:49:53.
In the course of time, the French also proposed a complete decimal system,
which was only put into use in a few respects. Shortly after the French Revo-
81
creasingly necessary to coordinate times and clocks internationally. Until then,
everyone used their own local time, related to the local geographical longitude,
in which the clock was basically set in such a way that on average throughout
the year the Sun was exactly in the south at noon. I digress briefly in order to
explain why I used the wording ‘on average’. It is not that simple in practice,
because there is the so-called ‘equation of time’, which is the property of the
Sun to be on the meridian too early or too late relative to the clock. This
difference varies in the course of a year. Its cause is that the Earth in its orbit
around the Sun does not have a constant speed and also because the rotation
axis of the Earth is not perpendicular to that orbital plane. The difference can
be up to 18 minutes, but of course averages out over a whole year. This can
be seen in the analemma, the distorted figure eight that is often depicted on
old maps and sundials. It shows up when we take a photograph of the Sun in
the sky every day at exactly the same time on the clock; if this is done for a full
year on a single plate, then the images of the Sun on it form this figure. The
vertical, long axis of the analemma is created by the seasons, which makes the
Sun high in the sky in the summer and low in the winter; the horizontal axis
by the equation of time.
In order to achieve greater uniformity, the idea had been put forward to
divide the Earth up into 24 zones of 15 ◦ in geographical longitude, whereby
the time within each zone would be the same everywhere and would differ by an
hour from the zones next to it. For practical reasons the zones were not chosen
as exactly 15 ◦ , but national borders were used. This system had originally
been proposed in 1879 by Sandford Fleming (1827–1915), a Scottish-born
Canadian engineer, but was also suggested by others independent of him. The
question was then where the meridian would run that would define longitude
zero. In October 1884, after long and bitter discussions, the decision was
made in Washington. The zero meridian ran through the Royal Observatory
in Greenwich and not through l’Observatoire de Paris. This ‘defeat’ was difficult
to accept for the leader of the French delegation, the astronomer Pierre Jules
César Janssen (1824–1907).
The Netherlands (and France and most of western continental Europe) are
in the the Central European Time zone, one hour later than Greenwich Mean
Time (nowadays called Universal Time). For the Netherlands the current situation actually is less favorable; on average (except for the equation of time) the
Sun is in Utrecht—for example, more or less the center of the Netherlands—on
the meridian at 12:39:32 (and one hour later during Daylight Savings Time).
Had the French been given the zero meridian, it would have been 11:49:53.
In the course of time, the French also proposed a complete decimal system,
which was only put into use in a few respects. Shortly after the French Revo-