at the focal point of a telescope he was designing
and realized that if he added crosshairs at that point
it would be easier to locate the center of the field of view.
He thus made the first telescopic sight.
Then Gascoigne realized that by placing two parallel hairs
and adjusting their separation using a fine screw
he could measure the size of the image in his view
and therefore calculate the relative size of objects in the sky.
He thus made the first micrometer.
Measuring comets
Richard Towneley improved
Gascoigne’s telescopic micrometer
and Robert Hooke used it
to measure the sizes of comets.
Henry Maudslay invented
the industrially practical screw-cutting lathe
and the first bench micrometer in about 1805,
accurate to one ten-thousandth of an inch.
Jean Laurent Palmer became so well known
for his handheld micrometer-screw calipers
that the device is called a palmer in French
and the Palmer screw in Spanish
and inspired similar devices around the world.
Measuring
If you can’t predict it
maybe you can measure it.
Maybe the measurement
can be shared, a length of cord
or a number of known lengths.
Maybe the measurement
will stand in the next century,
although few things
are truly constant.
Researchers at the University of Virginia report that
the Greenwich prime meridian, once bisecting the Airy Transit Circle
at the Royal Observatory in Greenwich, is now 102 meters to the east,
the original line having been deflected because the local direction
of gravitation affected the determination of the vertical.
Researchers at the University of Virginia report that the Greenwich prime meridian, once bisecting the Airy Transit Circle at the Royal Observatory in Greenwich, is now 102 meters to the east, the original line having been deflected because the local direction of gravitation affected the determination of the vertical.
See also in The book of science:
Readings on wikipedia: