This is very intuitive. Part of this cavity is the vacuum formed by the self-weight of the mercury.

Of course, this method does not necessarily require mercury. As long as it is a heavy liquid, there is no problem with water and alcohol.

However, because the mass of mercury is relatively heavy, the cavity formed is larger and more convenient for observation.

Before taking this class, Shen Mo's students already knew the concept of air, and Shen Mo also let them know through experiments that the oxygen in the air can burn... However, during this class, Shen Mo suddenly thought of another thing.

In history, Italian scientist Evangelista Toricheli... Of course, Shen Mo would never remember this broken name.

When he was doing this experiment, he found that the cavity sizes formed by mercury were different at different altitudes.

This is because he made a scale on the glass tube and climbed up the mountain while constantly measuring it.

As a result, he found that the higher the mountain he climbed, the smaller the cavity, that is, the vacuum part, would become.

So far, he discovered that the air pressure in high altitude is relatively low, and the closer it is to sea level, the higher the air pressure.

At this point, there was the first instrument to measure altitude in the world... When Shen Mo thought of this, he made an altitude instrument without hesitation.

Of course, the thing he made was not made of mercury glass tubes or something.

Instead, as historically, he made a small box made of thin iron.

When the box is vacuumed, it will inevitably be pressed by atmospheric pressure and deflated into it.

So Shen Mo made a steel frame to pull it apart so as not to flatten it by atmospheric pressure.

At the same time, he installed an instrument on it that can change the thickness of the box and convert it into a dial scale.

This instrument is basically the same as when later generations used glasses, which measure the curve of the lens. In fact, the principle and production process are very simple.

In this way, Shen Mo assembled into the world's first altitude meter.

Of course, when he made this thing, his purpose was to install it on a hot air balloon as an auxiliary device for hot air balloon flight.

Because if the visibility in the sky is too low or there is clouds, the hot air balloon may not know how high it is from the ground after it is launched.

So this vacuum altimeter began to serve in Shen Mo's hot air balloon troops.

But not long after, Shen Mo suddenly remembered this kind of altitude meter. The principle of measuring altitude is to use changes in air pressure.

So as long as it is made more precise, can it be used to measure atmospheric pressure?

As a result, this altimeter, which is not much larger than a compass, has become an instrument for measuring air pressure in a weather station.

So what does air pressure have to do with the climate?

The connection here is very big.

According to the news from Shen Mo's meteorological station, the results of the measurement of air pressure in Caotingshan have always been very unstable, which means that a storm is nearby!... If Shen Mo ordered the fleet to set off at this time, it is possible that before he saw an enemy, the landing troops would be beaten to pieces by the sea storm.

So Shen Mo decided to go to Caotingshan Meteorological Station in person to check it out.
Chapter completed!