In chapter 35 of Words of Radiance, Navani oversees the experiments around a levitating platform.
The experiment actually involves two wooden platforms (A and B), each having a set of stormlight infused gems. It is explained that the gems in A are linked to the gems in B (and viceversa), since they are halves of the same stone.
I'll give a brief summary of the experiment, but I don't have the book at hand right now (I may be editing this later to be more accurate):
- Platform A is set upon a moving wooden structure on wheels, so that it stays elevated from the ground. A is also connected to a set of ropes and pulleys, but those don't serve the purpose of keeping it up.
- Platform B (the tower) is laid out on the ground. On its surface there are mannequins, resembling soldiers.
- The moving structure on which platform A lies is slowly neared to B's location, until they are few meters (?) apart.
- The moving structure gets slowly removed from under platform A, which stays in place mid-air.
- Ardents start pulling on the ropes and lowering platform A from its midair position. This causes platform B to rise, effectively floating.
- At the end of the experiment, A is on the ground, while B is floating at A previous height (see points 1-4).
Navani explains that since the gems in the platforms are each half of the other, the platform are "connected in tandem". I don't recall correctly much of the explanation (again, I may come back to edit this later).
If we accept that platform B rises because A is taked down (since they are linked), why didn't platform B move when A was brought near?
In other words, I don't get why vertical movement affects both platforms, while horizontal movement can affect one (in my summary, platform A) and not the other.