24 April 2015
BUILD IT YOURSELF
By Mark McGuire
In 1643, Evangelista Torricelli discovered that "we live at the bottom of a sea of air,"
and the pressure of the air could be measured with a simple column of water or
mercury. In 1648, Blaise Pascal found differences in pressure with only slight
elevation changes, leading to the idea that air has weight.
Changes in this pressure acting on evacuated bellows can be made to trace a line on
a clockwork-powered drum, indicating fluctuations in atmospheric pressure as shown
in Photo 1. You can still buy these devices which are credited to Lucien Vidi, who (in
1844) invented the practical barograph. They have been much improved, but still
require a steady platform, winding of the clockwork, refreshing of the special ink (that
must remain fluid until it hits the paper, then quickly dries), and renewing of the chart
paper. They are also expensive.
BUILD YOUR OWN ARDUINO
■ PHOTO 1.