3.19 Inventions, Excavations and Findings

Through lightning in the box gold and silver are melted,
the two captives will devour each other.
The greatest one of the city stretched
when the fleet travels under water. (III-13)

This quatrain refers to some inventions that you would call «modern» inventions. For example, the «box with the flickering light» refers to the taming and controlling of electricity. «Gold and silver in the box being melted» refers to some of the applications of electrical technology, such as electroplating things with gold and such.

And how this is in turn led to technology such as communications technology using microchips and such as this which in turn is what is used to communicate with what you call «submarine» – the fleet of submarines that each country has. So I was just simply trying to produce a picture of all the many wondrous inventions I saw for the future.
The part that says, «the two captives will devour each other» has to do with, yes, the opposite energies involved because they have to be balanced for it to work. And so they, in a sense, devour each other in that they are balanced.

The rock holds in its depths white clay
which will come out milk-white from a cleft.
Needlessly troubled people will not dare touch it,
unaware that the foundation of the earth is of clay. (Ι-21)

Somewhere in western North America there will be some miners digging for ore. And this ore they find will be a different ore than that which they are looking for. They will be afraid that it is some sort of radioactive material brought in or introduced by a meteorite centuries ago – «needlessly troubled people will not dare touch it». But there is no need for alarm because this material, although it will end up being a new element to put on the periodic table, will not be harmful for mankind and can be put to good use.
The new ore was brought in by a meteorite.

Ambassadors of the Tuscan language
will cross the Alps and the sea in April and May.
The man of he calf will deliver an oration,
not coming to wipe out the French way of life. (VII-20)

I saw new healthier ways to grow food outside, and inside through the harshest times of the year. There are ways of cultivating without the need for sunlight or earth. And new resources for energy that are nonpolluting. I saw methods of using the electromagnetic field and other connective forms of energy to make things healthier, more efficient, and less expensive.