Picard wasn’t the first or the last to
measure a meridian arc.
Francesco Maurolico described this method in 1543,
and it is thought to have been suggested by Eratosthenes.
Gemma Frisius invented triangulation in 1533.
Willebrord Snellius (known as Snell) developed the math
for measuring by triangulation from city to city in 1617,
which he did in an attempt to follow Maurolico’s
method,
although his result not as accurate as Picard’s.
William Gascoigne had invented the micrometer
and the telescopic sight with crosshairs in 1638.
All Jean Picard did was put it all together.
Picard measured his baseline with wooden rods,
attached Gascoigne’s telescope and micrometer to a
quadrant
to measure his angles, used Snell’s math
with John Napier’s logarithms in his calculations
and achieved enough accuracy to be considered
the first modern measurement of the polar radius.
Instruments
If Archimedes had a lever long enough
and a fulcrum on which to place it
then he could have moved the world.
If I had a reason strong enough,
a judgment clear enough,
a meaning near enough
then I could help people
put aside their differences
and feel compassion for each other.
We live on a small fragile world,
in which greed has measurable harm
and generosity measurable benefit.
Jean Picard corresponded with Huygens, Newton, Ole
Rømer who made the Rømer temperature scale, Rasmus
Bartholin who discovered birefringence, and Giovanni Cassini, who
calculated the distance between Earth and Mars. Picard used
Christiaan Huygens’ pendulum clock in measuring the right
ascension of celestial objects in 1673, and his measurement of the
earth was useful to Isaac Newton in his theory of universal
gravitation.
Jean Picard corresponded with Huygens, Newton, Ole Rømer who made the Rømer temperature scale, Rasmus Bartholin who discovered birefringence, and Giovanni Cassini, who calculated the distance between Earth and Mars. Picard used Christiaan Huygens’ pendulum clock in measuring the right ascension of celestial objects in 1673, and his measurement of the earth was useful to Isaac Newton in his theory of universal gravitation.
See also in The book of science:
Readings on wikipedia: