1638

Micrometer

• William Gascoigne discovered a spider’s web
• 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.