How Does Lorentz Theory Address the Concept of Velocity Becoming Zero?

[bos3yed651]

This is my first thread. I hope I do it right. I just started reading the book Special Relativity by W.Rindler. And as I was reading it, I stumbled upon a pickle. So in Lorentz theory, it says, supposedly we could measure the original to-and-fro time T2 directly with a clock, and suppose we then move the arm L2 along with ether so that v becomes zero. My question is how v became zero and I know that the question might sound stupid to some but please dazzle me.
A pdf of the page is attached along. Thank you for your time :)

 

[Ibix]

$v$ is the velocity of the experiment relative to the (supposed) ether. If the experiment is moving along with the ether then their relative velocity is zero.

 

[bos3yed651]

thanks, made my a day a lot easier.