These ever varying elements represent an ever varying elliptic orbit, - not an orbit which the planet actually describes through its whole course, but an ideal one in which it is moving at each instant, and which continually adjusts itself to the actual motion of the planet at the instant.
The stationary wave system adjusts itself so that its motion agrees with that of the sounder, which is therefore not exactly at a node.
Thompson and others have shown however that they contain both neutral and charged molecules in a relative proportion which adjusts itself continuously, so that even neutral molecules may partake of the translatory motion which they gained while carrying a charge.
In reality, the tension adjusts itself automatically to the weight to be supported at the various levels.
He then adjusts the instrument so that the cross threads coincide with their images reflected from the surface of the quicksilver.