The lid and its hanging loop at the top.
On my rain lamp the lid will not lift until the lid has been unscrewed and the bulb had been removed, and even then will not completely separate from the cage part unless the bulb wires are removed. But it is dangerous and unnecessary to remove the bulb wires.
Also, although the photograph below shows a bulb in the lid, ordinarily there would be no reason to put the bulb back into the lifted lid, except maybe to test if altered electrical connections are functioning before screwing the lid back into place.
These posts do more than support, however. All are hollow and perform critical functions.
Looking at the underside of the "cage" part, and proceding in counterclockwise order,
here is a description of these three posts:
Note that the electrical post is threaded at the top. All three posts are threaded for unscrewing, but they are also all sealed against oil leakage, so the posts shouldn't be unscrewed since that would presumably damage the lamp and affect its operation.
Note the seal around the bottom of the pumping post, where the oil tube goes in. Rain lamps were apparently made with high economy; the post connections that didn't need to be sealed weren't sealed. Specifically, whereas the tops of all the posts needed to be sealed where they enter the top basin to prevent oil from leaking downwards, the only post that needed to be sealed at the bottom was the pumping post, and that was the only post that was in fact sealed. Sealing is obviously unimportant at the bottom of the drain, and where only electrical wires are passing through at the bottom.
Unless somebody builds a different type of rain lamp, all rain lamps must have a tube that carries the oil back to the top. Disneyland's rain lamp had no outer posts, but it had a central post that must have served the same function. For such floor-to-ceiling rain lamps, a more clever solution would be to run the oil tube under the floor, behind the wall, and above the ceiling so that there appears to be no recirculation mechanism. Another solution would be to make a large enough reservoir at the top that the oil can drip all day without running out. A more radical solution would be to make at least some of the fibers hollow so that the oil flowed up the same fibers inside while dripping down on the outside. Another innovation might be to use the hourglass mechanism so that the rain lamp could be turned upside down after all the oil ran to one end. That way, no pump would be necessary, although such a lamp would require both oil basins to be sealed, and of course would have a limited time of flow.
Note that the top of this post is sealed, as it needs to be, but the bottom is not sealed and doesn't need to be.
The bottom basin is mostly uninteresting, structurally. Screw holes at the top of the sides of the bottom basin allow the cage part of the lamp to be fastened to the bottom basin. On my rain lamp, the bottom basin has a bolt in the center of the bottom that is sealed the same way that the oil posts are sealed at their tops. If one removes the felt bottom, the bottom end of this bolt can be seen. I'm not sure why this hole was put into the basin at all, since it serves no purpose and has to be sealed at additional effort. Some rain lamps like my Johnson Industries lamp also have a decorative band encircling the top of bottom basin.
