Evidence for significant differences in the relative amounts of silicates vs. gas compounds of volatile elements between the terrestrial planets and the moons of the gas giants comes from calculating the bodies' .

Densities

Explanation:

A planet is a body which orbits the Sun (or father's it's sun) directly and is massive enough to show a hydrostatic equilibrium ( a spheroid) and be resilient in dominating its orbit

What comes to mind as we mention the word planet is specifically, the eight major bodies of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Note that  Pluto once was considered a planet from the 17th century until 2006 and has now been reclassified as a dwarf planet.

Density is the measure with ratio of one quantity to another quantity.

It can quantitatively be a measure of the mass of matter contained by a unit volume.

The knowledge of density of gases comes in handy to calculate the relative amount of substances.

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.