This led to curious speculations concerning its probable metallic composition, and the possible existence of vast quantities of such heavy elements as gold in the frame of the planet.

But more recent, and probably more correct, computations place Mercury third in the order of density among the members of the solar system, the earth ranking as first and Venus as second.

Mercury's density is now believed to be less than the earth's in the ratio of 85 to 100.

Accepting this estimate, we find that the force of gravity upon the surface of Mercury is only one third as great as upon the surface of the earth--i.e., a body weighing 300 pounds on the earth would weigh only 100 pounds on Mercury.
This is an important matter, because not only the weight of bodies, but the density of the atmosphere and even the nature of its gaseous constituents, are affected by the force of gravity, and if we could journey from world to world, in our bodily form, it would make a great difference to us to find gravity considerably greater or less upon other planets than it is upon our own.

This alone might suffice to render some of the planets impossible places of abode for us, unless a decided change were effected in our present physical organization.
One of the first questions that we should ask about a foreign world to which we proposed to pay a visit, would relate to its atmosphere.