We plan to produce a large number of videos
ilustrating the experiments we are performing once in a while
in our laboratories. Here is one of the first: "The
Baroscope" demonstrating that air has weight.
Towards the middle of 17th century the
scientist were ready to explain why mine water could not be sucked
from surface to more than 32 ft. Evangelista Torricelli figured
out that once the water column pressure become equals the atmospheric
pressure the water will stop raising towards the pump. Torricelli
realized the water is `not sucked up` but works like a weight
on a scale in balance with another weight: the atmospheric air
The main concern with the simple mercury barometer,
shown at right, is the sturdiness of the glass tube ; if breaks
the poisonous heavy metal will go all over and it will be very hard
to get rid of it. The large total surface area of the small droplets
will permit fast reaching equilibrium for the partial pressure of
mercury vapors. Everybody will bread those vapors.
When the atmospheric pressure change, it is impossible to account
for change in the level of mercury in the reservoir. At least a
ruler has to be attached to anable to record the position of the
mercury in the tube and so the atmospheric pressure.
There is as much as needed sophistication in the mercury barometer
shown at left: no bottle at the bottom but an "U" turn.
A precise measurement of the changes in mercury column can be
made. A ruler is built in. The fragile and dangerous mercury tube
is protected by the wooden box. The only thing missing is a thermometer
(inside the box) to permit corrections for thermal expansion of
Niagara Science Museum - 3625 Highland Ave.
Niagara Falls, NY 14305
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